AON Aon PLC

DESCRIPTION OF THE SECURITIES

The following description of the particular terms of the Securities offered by this prospectus supplement and, to the extent inconsistent therewith, replaces the description of the general terms and provisions of the Securities set forth under “Description of Debt Securities and Guarantees” in the accompanying prospectus. Terms used herein that are otherwise not defined have the meanings given to them in the accompanying prospectus.

Aon Corporation and AGH will co-issue $        aggregate principal amount of    % senior notes due 20    (the “ 20    Notes”) and $        aggregate principal amount of    % senior notes due 20    (the “ 20    Notes” and, together with the 20    Notes, the “Notes”) pursuant to the amended and restated indenture, dated April 1, 2020, among Aon Corporation, as an issuer, Aon plc, AGL and AGH, as guarantors, and The Bank of New York Mellon Trust Company, N.A., as trustee (the “Trustee”) (amending and restating the indenture, dated December 3, 2018, among Aon Corporation, as an issuer, AGL, as guarantor, and the Trustee), as amended and supplemented by a supplemental indenture, to be dated as of             , 2022, among Aon Corporation and AGH, as co-issuers, Aon plc and AGL, as guarantors, and the Trustee. We refer to the amended and restated indenture, as amended and supplemented, as the indenture. The following is a summary of the material provisions of the indenture. It does not include all of the provisions of the indenture. We urge you to read the indenture because it, not this description, defines your rights. The terms of the Securities include those stated in the indenture and those made part of the indenture by reference to the Trust Indenture Act of 1939, as amended (the “TIA”). A copy of the indenture may be obtained from the Issuers or the Trustee.

The Issuers will issue the Notes in fully registered form in denominations of $2,000 and integral multiples of $1,000 in excess thereof. The Trustee will initially act as paying agent and registrar for the Notes. The Notes may be presented for registration of transfer and exchange at the offices of the registrar. The Issuers may change the paying agent and registrar without notice to holders of the Notes. It is expected that the Issuers will pay principal and interest (and premium, if any) on the Notes (and, as necessary, each Guarantor will pay such amounts in relation to its applicable Guarantee) at the Trustee’s corporate office or by wire transfer, if book-entry at The Depository Trust Company (“DTC”).

Co-Issuance

The Issuers are co-issuers of the Notes and, as such, the Notes of each series will be joint and several obligations of each of the Issuers.

Principal, Maturity and Interest

The 20    Notes will mature on                 , 20     . The 20    Notes will mature on                 , 20     . $        in aggregate principal amount of 20    Notes and $        in aggregate principal amount of 20    Notes will be issued in this offering. After the issue date of the Notes, additional notes having the same terms and conditions as the Notes of the applicable series in all respects (other than the issue date, public offering price, and to the extent applicable, first date of interest accrual and first interest payment date of such notes) (“Additional Notes”) may be issued from time to time; provided, however, that if the Additional Notes of such series are not fungible with the Notes of such series for U.S. federal income tax purposes, the Additional Notes of such series will have a separate CUSIP number. The applicable series of Notes and any Additional Notes of such series that are actually issued will be treated as a single class for all purposes under the indenture, including, without limitation, as to waivers, amendments, redemptions and any applicable offers to purchase. Unless the context otherwise requires, for all purposes of the indenture and this “Description of the Securities,” references to the Notes include any Additional Notes of such series actually issued and references to the Notes of a series include any Additional Notes of such series actually issued.

Interest on the 20    Notes will accrue at the rate of    % per annum and will be payable semi-annually in arrears in cash on each                and                , commencing on                , 2022, to the persons who are

S-18

registered holders at the close of business on                or                , as the case may be, immediately preceding the applicable interest payment date. Interest on the 20    Notes will accrue at the rate of    % per annum and will be payable semi-annually in arrears in cash on each                and                , commencing on                , 2022, to the persons who are registered holders at the close of business on                or                , as the case may be, immediately preceding the applicable interest payment date. Interest on the Notes of a series will accrue from the most recent date to which interest has been paid or, if no interest has been paid, from and including the date of issuance to but excluding the actual interest payment date.

Interest will be computed on the basis of a 360-day year composed of twelve 30-day months.

Optional Redemption

Prior to                , 20                (                month(s) prior to the 20                Notes maturity date) (the “20    Par Call Date”), and prior to                , 20                (                month(s) prior to the 20                Notes maturity date) (the “20    Par Call Date”), the Issuers may redeem the 20    Notes and/or the 20    Notes at their option, in whole or in part, at any time and from time to time, at a redemption price (expressed as a percentage of the principal amount and rounded to three decimal places) equal to the greater of:

plus, in either case, accrued and unpaid interest on the principal amount of the Notes of such series being redeemed to the redemption date.

On or after the applicable Par Call Date, the Issuers may redeem the 20    Notes and/or the 20    Notes, in whole or in part, at any time and from time to time, at a redemption price equal to 100% of the principal amount of the Notes of such series being redeemed plus accrued and unpaid interest thereon to the redemption date.

“Treasury Rate” means, with respect to any redemption date, the yield determined by the Issuers in accordance with the following two paragraphs:

The Treasury Rate shall be determined by the Issuers after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the redemption date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Issuers shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the redemption date to the Par Call Date for the applicable series of Notes (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the Par Call Date on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining

S-19

Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the redemption date.

If on the third business day preceding the redemption date H.15 is no longer published, the Issuers shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such redemption date of the United States Treasury security maturing on, or with a maturity that is closest to, the Par Call Date, as applicable. If there is no United States Treasury security maturing on the Par Call Date but there are two or more United States Treasury securities with a maturity date equally distant from the Par Call Date, one with a maturity date preceding the Par Call Date and one with a maturity date following the Par Call Date, the Issuers shall select the United States Treasury security with a maturity date preceding the Par Call Date. If there are two or more United States Treasury securities maturing on the Par Call Date or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Issuers shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time, of such United States Treasury security, and rounded to three decimal places.

The Issuers’ actions and determinations in determining the redemption price shall be conclusive and binding for all purposes, absent manifest error.

Notice of any redemption will be mailed or electronically delivered (or otherwise transmitted in accordance with the depositary’s procedures) at least 10 days but not more than 60 days before the redemption date to each holder of Notes to be redeemed. In the case of a partial redemption, selection of the Notes for redemption will be made pro rata, by lot or by such other method as the Trustee in its sole discretion deems appropriate and fair. No Notes of a principal amount of $2,000 or less will be redeemed in part. If any Note is to be redeemed in part only, the notice of redemption that relates to the Note will state the portion of the principal amount of the Note to be redeemed. A new Note in a principal amount equal to the unredeemed portion of the Note will be issued in the name of the holder of the Note upon surrender for cancellation of the original Note. For so long as the Notes are held by DTC (or another depositary), the redemption of the Notes shall be done in accordance with the policies and procedures of the depositary.

Unless the Issuers defaults in payment of the redemption price, on and after the redemption date interest will cease to accrue on the Notes or portions thereof called for redemption.

Notwithstanding the foregoing, installments of interest on Notes being redeemed that are due and payable on interest payment dates falling on or prior to a redemption date will be payable on the interest payment date to the registered holders as of the close of business on the relevant record date according to such Notes and the indenture.

Guarantees

Under the Guarantees, each Guarantor will fully, unconditionally and irrevocably guarantee, jointly and severally, the due and punctual payment of the principal, interest, premium (if any) and all other amounts due under the indenture and on the Notes when the Notes become due and payable, whether at maturity, pursuant to optional redemption, by acceleration or otherwise, in each case after any applicable grace periods or notice requirements, according to the terms of the Notes.

The obligations of each Guarantor under its Guarantee will be unconditional, regardless of the enforceability of the Notes, and will not be discharged until all obligations under the Notes and the indenture are satisfied.

S-20

Holders of the Notes may proceed directly against Aon plc and/or AGL under the Guarantees if an event of default affecting the Notes occurs without first proceeding against the Issuers.

Ranking

The Notes will be:

Each Guarantee will be:

See “Risk Factors—The Notes will be effectively subordinated to all of the applicable Issuer’s existing and future secured indebtedness (to the extent of the value of the assets securing any such indebtedness) and to the existing and future indebtedness of the applicable Issuer’s subsidiaries, and each Guarantee will be effectively subordinated to all of the applicable Guarantor’s existing and future secured indebtedness (to the extent of the value of the assets securing any such indebtedness) and to the existing and future indebtedness of such Guarantor’s subsidiaries.” As of December 31, 2021, the Issuers had no secured indebtedness for borrowed money and approximately $12,355 million of consolidated outstanding indebtedness and other liabilities, including accounts payable and accrued liabilities, pension and other post-retirement and post-employment liabilities, non-current operating lease liabilities, deferred tax liabilities, other current liabilities and non-current liabilities, but excluding intercompany liabilities and fiduciary liabilities. The Notes will be structurally subordinated to all of the existing and future secured and unsecured indebtedness and other liabilities of the applicable Issuer’s subsidiaries. As of December 31, 2021, the Issuers’ subsidiaries had approximately $5,402 million of outstanding indebtedness and other liabilities, including accounts payable and accrued liabilities, pension and other post-retirement and post-employment liabilities, non-current operating lease liabilities, deferred tax liabilities, other current liabilities and non-current liabilities, but excluding intercompany liabilities and fiduciary liabilities. These liabilities constitute approximately 43.7% of the Issuers’ total consolidated liabilities. As of December 31, 2021, the Guarantors had no secured indebtedness for borrowed money and approximately $16,373 million of consolidated outstanding indebtedness and other liabilities, including accounts payable and accrued liabilities, pension and other post-retirement and post-employment liabilities, non-current operating lease liabilities, deferred tax liabilities, other current liabilities and non-current liabilities, but excluding intercompany liabilities and fiduciary liabilities. As of December 31, 2021, the

S-21

subsidiaries of the Guarantors had no secured indebtedness for borrowed money and approximately $12,478 million of outstanding indebtedness and other liabilities, including accounts payable and accrued liabilities, pension and other post-retirement and post-employment liabilities, non-current operating lease liabilities, deferred tax liabilities, other current liabilities and non-current liabilities, but excluding intercompany liabilities and fiduciary liabilities. These liabilities constitute approximately 76.2% of the Guarantors’ total consolidated liabilities.

Payment of Additional Amounts

Payments made by a Guarantor in respect of its Guarantee will be made free and clear of and without withholding or deduction for or on account of any present or future income, stamp or other tax, duty, levy, impost, assessment or other governmental charge of any nature whatsoever imposed or levied by or on behalf of the government of Ireland or the United Kingdom, as applicable, or, in each case, by any authority or agency therein or thereof having the power to tax, which we refer to collectively as “Taxes,” unless such Guarantor is required to withhold or deduct Taxes by law.

If a Guarantor is required to withhold or deduct any amount for or on account of Taxes from any payment made with respect to its Guarantee, such Guarantor will pay such additional amounts as may be necessary so that the net amount received by each beneficial owner (including additional amounts) after such withholding or deduction will not be less than the amount the beneficial owner would have received if the Taxes had not been withheld or deducted; provided that no additional amounts will be payable with respect to Taxes:

S-22

nor shall additional amounts be paid with respect to any payment in respect of a Guarantee to any such holder who is a fiduciary or a partnership or who is other than the sole beneficial owner of such payment to the extent a beneficiary or settlor with respect to such fiduciary or a member of such partnership or a beneficial owner would not have been entitled to such additional amounts had it been the holder of the Note.

For avoidance of doubt, no additional amounts shall be paid with respect to or on account of any present or future income, stamp or other tax, duty, levy, impost, assessment or other governmental charge of any nature whatsoever imposed or levied by or on behalf of the government of the United States, the United Kingdom or any other taxing authority relating to payments by the Issuers under the Notes.

All references in this prospectus supplement and the accompanying prospectus, other than under “Description of Debt Securities and Guarantees—Defeasance” in the accompanying prospectus, to the payment of the principal of or premium, if any, or interest, if any, on or the net proceeds received on the sale or exchange of, any Notes or any payment made under a Guarantee shall be deemed to include additional amounts to the extent that, in that context, additional amounts are, were or would be payable.

Each Guarantor’s obligations to pay additional amounts if and when due will survive the termination of the indenture and the payment of all other amounts in respect of the Notes.

Non-U.S. Holders (as defined under “Material U.S. Federal Income Tax Consequences—Tax Consequences Applicable to Non-U.S. Holders—Definition of a Non-U.S. Holder”) should refer to “Material U.S. Federal Income Tax Consequences—Tax Consequences Applicable to Non-U.S. Holders” for a discussion of U.S. federal withholding taxes that may be imposed on payments under the Notes and possible exemptions from, or reductions of, such withholding taxes.

Optional Tax Redemption

The Issuers may redeem the Notes of a series in whole, but not in part, at their option at any time prior to maturity, upon the giving of not less than 10 nor more than 90 days’ notice of tax redemption to the holders, at a redemption price equal to the principal amount of the Notes of such series plus accrued and unpaid interest, if any, to the redemption date, if:

S-23

No notice of any such redemption may be given earlier than 90 days prior to the earliest date on which a Guarantor would be obligated to pay any additional amounts.

Prior to the delivery of any notice of redemption, the Issuers will deliver to the Trustee an officers’ certificate stating that it is entitled to effect or cause a redemption and setting forth a statement of facts showing that the conditions precedent of the right so to redeem or cause such redemption have occurred, and in the case of a redemption based on an opinion of independent counsel referred to in the second bullet above, such independent counsel’s opinion. Delivery of any notice of redemption will be conclusive and binding on the holders of the Securities being redeemed.

Any notice of redemption will be irrevocable once an officers’ certificate has been delivered to the Trustee.

Agreed Tax Treatment

Although the Notes are co-issued by Aon Corporation and AGH and, therefore, each Issuer is liable for repayment of the Notes in their entirety, the net proceeds of the offering of the Notes will be received solely by Aon Corporation and Aon Corporation will incur all of the underwriting discounts and commissions with respect to the Notes. In addition, Aon Corporation has agreed to make all interest payments and principal repayments on the Notes. As discussed further under “Material U.S. Federal Income Tax Consequences”, we intend to treat Aon Corporation as the sole obligor under the Notes for U.S. federal tax purposes and any interest paid by Aon Corporation on the Notes as U.S.-source income for U.S. federal income tax purposes. If we intend to cause AGH to become an obligor (in whole or in part) under the Notes or to otherwise change our present U.S. federal tax treatment of interest payments on the Notes, Aon will advise Holders on Aon’s website.

Governing Law

The indenture and the Securities will be governed by, and construed in accordance with, the laws of the State of New York.

Concerning Our Relationship with the Trustee

The Issuers and the Guarantors have commercial deposits and custodial arrangements with The Bank of New York Mellon Trust Company, N.A. (“BNYM”) and may have borrowed money from BNYM or its affiliates in the normal course of business. The Issuers and the Guarantors may enter into similar or other banking relationships with BNYM or its affiliates in the future in the normal course of business. In addition, the Issuers and the Guarantors have provided brokerage and other insurance services in the ordinary course of their business for BNYM or its affiliates. BNYM may also act as trustee with respect to other debt securities issued by the Issuers and the Guarantors.

Offers to Purchase; Open Market Purchases

Neither the Issuers nor any Guarantor is required to make any sinking fund payments or any offers to purchase with respect to the Notes or the Guarantees. An Issuer or a Guarantor may at any time and from time to time purchase Notes in the open market or otherwise.

S-24

DESCRIPTION OF DEBT SECURITIES AND GUARANTEES

In this description, references to “holders” mean those who own debt securities and the related guarantees registered in their own names, on the books that the registrar maintains for this purpose, and not those who own beneficial interests in debt securities and the related guarantees registered in “street name” or issued in book-entry form and held through one or more depositaries.

The following description, together with the additional information we include in any applicable prospectus supplement or free writing prospectus, summarizes certain general terms and provisions of the debt securities that may be offered pursuant to this prospectus. When we offer to sell a particular series of debt securities, we will describe the specific terms of the series in a supplement to this prospectus. We will also indicate in the applicable prospectus supplement to what extent the general terms and provisions described in this prospectus apply to a particular series of debt securities.

Aon plc Debt Securities

Aon plc may issue senior debt securities (the “Aon plc debt securities”) under an indenture (the “Aon plc indenture”), among Aon plc, as issuer, AGL, AGH and Aon Corporation, as guarantors (the “Aon plc guarantors”) in respect of certain series of Aon plc debt securities, and The Bank of New York Mellon Trust Company, N.A., as trustee (the “trustee”).

Any Aon plc debt securities issued under the Aon plc indenture will constitute unsubordinated debt of Aon plc. Any guarantee that AGL, AGH and Aon Corporation, as the Aon plc guarantors, issue under the Aon plc indenture will constitute unsubordinated obligations of AGL, AGH and Aon Corporation (each, an “Aon plc debt guarantee”).

AGH Debt Securities

AGH may issue senior debt securities (the “AGH debt securities”) under an indenture (the “AGH indenture”), among AGH, as issuer, Aon plc, AGL and Aon Corporation, as guarantors (the “AGH guarantors”) in respect of certain series of AGH debt securities, and the trustee.

Any AGH debt securities issued under the AGH indenture will constitute unsubordinated debt of AGH. Any guarantee that Aon plc, AGL or Aon Corporation, as the AGH guarantors, issue under the AGH indenture will constitute unsubordinated obligations of Aon plc, AGL and Aon Corporation (each, an “AGH debt guarantee”).

Aon Corporation Debt Securities

Aon Corporation may issue senior debt securities (the “Aon Corporation debt securities”) under an indenture (the “Aon Corporation indenture”), among Aon Corporation, as issuer, Aon plc, AGL and AGH, as guarantors (the “Aon Corporation guarantors”) in respect of certain series of Aon Corporation debt securities, and the trustee. There are currently three existing Aon Corporation indentures: (i) the Second Amended and Restated Indenture, dated April 1, 2020 (amending and restating the Amended and Restated Indenture, dated April 2, 2012) (originally dated January 13, 1997); (ii) the Second Amended and Restated Indenture, dated April 1, 2020 (amending and restating the Amended and Restated Indenture, dated April 2, 2012) (originally dated September 10, 2010); and (iii) the Amended and Restated Indenture, dated April 1, 2020 (amending and restating the Indenture, dated December 3, 2018).

Any Aon Corporation debt securities issued under the Aon Corporation indenture will constitute unsubordinated debt of Aon Corporation. Any guarantee that Aon plc, AGL or AGH, as the Aon Corporation

10

guarantors, issue under the Aon Corporation indenture will constitute unsubordinated obligations of Aon plc, AGL and AGH (each, an “Aon Corporation debt guarantee”).

In this description:

The terms of each series of debt securities will be established by or pursuant to a resolution of our board of directors and set forth or determined in the manner provided in a resolution of our board of directors, in an officers’ certificate or by a supplemental indenture. The terms of any debt securities and, if applicable, the guarantees will include those stated in the applicable indenture and those made part of that indenture by reference to the Trust Indenture Act of 1939 (the “Trust Indenture Act”). The debt securities will be subject to all those terms, and we refer prospective purchasers and holders of debt securities and guarantees to the applicable indenture and the Trust Indenture Act for a statement of those terms. The debt securities will be described in a prospectus supplement relating to such series (including any pricing supplement or term sheet).

The following summaries of various provisions of the debt securities, the indentures and the guarantees are not complete. They do not describe certain exceptions and qualifications contained in the debt securities, the indentures and the guarantees, and are qualified in their entirety by reference to the provisions of the debt securities, the indentures and the guarantees. Unless we otherwise indicate, capitalized terms have the meanings assigned to them in the applicable indenture.

An applicable prospectus supplement will specify the issuer, the guarantors, if any, and whether the debt securities are to be guaranteed. The debt securities may be issued as part of units consisting of debt securities and other securities that may be offered under this prospectus. If debt securities are issued as part of units of debt securities and other securities that may be issued under this prospectus, an applicable prospectus supplement will describe any applicable material federal income tax consequences to holders.

General

The debt securities will be unsecured obligations of the applicable issuer. None of the indentures limit the amount of debt securities that the issuer may issue. Each indenture provides that the issuer may issue debt securities from time to time in one or more series.

The debt securities and any debt guarantees will be unsecured and unsubordinated obligations of the applicable issuer and will rank equally in right of payment with such issuer’s other unsecured and unsubordinated obligations. Because each of Aon plc, AGL, AGH and Aon Corporation is a holding company, the holders of debt securities and debt guarantees may not receive assets of the applicable issuer’s subsidiaries in a liquidation or recapitalization until the claims of such subsidiaries’ creditors and any insurance policyholders (in the case of insurance subsidiaries) are paid, except to the extent that the applicable issuer may have recognized claims against such subsidiaries. In addition, certain regulatory laws limit some of such subsidiaries from making payments to the applicable issuer of dividends and on loans and other transfers of funds.

11

An applicable prospectus supplement will describe the specific terms relating to the series of debt securities being offered. These terms will include some or all of the following:

If an issuer denominates the purchase price of a series of debt securities in a non-U.S. dollar currency or currencies or a non-U.S. dollar currency unit or units, or if the principal of, any premium and interest on any series of debt securities is payable in a non-U.S. dollar currency or currencies or a non-U.S. dollar currency unit or units, an applicable prospectus supplement will describe any special U.S. federal income tax considerations.

The issuer will pay principal and any interest, premium and additional amounts in the manner, at the places and subject to the restrictions set forth in the applicable debt securities, the applicable indenture and any applicable prospectus supplement. The issuer will not impose a service charge for any transfer or exchange of debt securities, but it may require payment of a sum sufficient to cover any tax or other governmental charge that may be imposed. (Section 2.05 of the indentures).

Unless otherwise indicated in an applicable prospectus supplement, each issuer will issue debt securities in fully registered form, without coupons, in denominations of $1,000 or multiples of $1,000. (Sections 2.01 and 2.04 of the indentures).

12

The issuer may offer to sell at a substantial discount below their stated principal amount, debt securities bearing no interest or interest at a rate that, at the time of issuance, is below the prevailing market rate. An applicable prospectus supplement will describe any special U.S. federal income tax considerations applicable to any of those discounted debt securities.

The issuer may offer to sell debt securities in which the principal or interest will be determined by reference to one or more currency exchange rates, commodity prices, equity indices or other factors. The principal amount or payment of interest applicable to those debt securities may be greater than or less than the amount of principal or interest otherwise payable, depending upon the value of the applicable currency, commodity, equity index or other factor on the date on which that principal or interest is due. An applicable prospectus supplement will describe the methods used to determine the amount of principal or interest payable on any date, the currencies, commodities, equity indices or other factors to which the amount payable on that date is linked and certain additional tax considerations applicable to those debt securities.

The indentures do not restrict the issuers’ ability to incur unsecured indebtedness or, subject to the restrictions described in “ —Consolidation and Merger,” to engage in reorganizations, restructurings, mergers, consolidations or similar transactions that have the effect of increasing the issuers’ indebtedness. Accordingly, unless an applicable prospectus supplement states otherwise, neither the debt securities nor any guarantees will contain any provisions that afford holders protection against the issuers or, if applicable, the guarantors incurring unsecured indebtedness or engaging in certain reorganizations or transactions. As a result, any of the issuers could become highly leveraged.

Events of Default

With respect to any series of debt securities, “event of default” means any of the following:

13

If there is a continuing event of default with respect to any outstanding series of debt securities, the applicable trustee or the holders of at least 25% of the outstanding principal amount of the debt securities of that series may require the issuer or, if applicable, the guarantors to pay immediately the principal (or, if the debt securities of that series are discount securities, that portion of the principal amount as may be specified in the terms of that series) of and accrued and unpaid interest, if any, on all debt securities of that series. However, at any time after that trustee or the holders, as the case may be, declare an acceleration with respect to debt securities of any series, but before the applicable person has obtained a judgment or decree for payment of the money, the holders of a majority in principal amount of the outstanding debt securities of that series may, under certain conditions, cancel such acceleration if (i) all events of default (other than the non-payment of accelerated principal) with respect to such debt securities have been cured or (ii) all such events of default have been waived, each as provided in the applicable indenture. (Section 6.01 of the indentures). For information as to waiver of defaults, see “ —Modification and Waiver.” The particular provisions relating to acceleration of the maturity of a portion of the principal amount of such debt securities that are discount securities triggered by an event of default shall be described in an applicable prospectus supplement.

Each indenture provides that, subject to the duties of the applicable trustee to act with the required standard of care, if there is a continuing event of default, the applicable trustee need not exercise any of its rights or powers under the indenture at the request or direction of any of the holders of debt securities, unless those holders have offered to the applicable trustee security or indemnity reasonably satisfactory to it. (Section 7.02 of the indentures). Subject to those provisions for security or indemnification of the applicable trustee and certain other conditions, the holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the applicable trustee or exercising any trust or power that trustee holds, in each case, with respect to the debt securities of that series. (Section 6.06 of the indentures).

No holder of any debt security of any series will have any right to institute any proceeding with respect to any indenture or for any remedy thereunder unless:

However, the holder of any debt security will have an absolute and unconditional right to receive payment of the principal of, and any premium or interest on, that debt security on or after the date or dates they are to be paid as expressed in or pursuant to that debt security and to institute suit for the enforcement of any such payment. (Section 6.04 of the indentures).

Each indenture provides that the applicable trustee shall provide notice to the holders of debt securities of any series within 90 days of the occurrence of any default with respect to such debt securities known to such trustee, except that the trustee need not provide holders of such debt securities notice of any default (other than the non-payment of principal or any premium, interest or additional amounts) if such default has been cured and such trustee considers it in the interest of the holders of such debt securities not to provide that notice. (Section 6.07 of the indentures).

14

Consolidation and Merger

Each indenture provides that each of the issuer and the guarantors may consolidate with or merge or convert into, or convey, transfer or lease its or their properties or assets substantially as an entirety to, another person without the consent of any debt security holders if, along with certain other conditions set forth in the indentures:

It is possible that a merger, transfer, lease or other transaction could be treated for U.S. federal income tax purposes as a taxable exchange by the holders of debt securities or guarantees for new securities, which could result in holders of debt securities or guarantees recognizing taxable gain or loss for U.S. federal income tax purposes. A merger, transfer, lease or other transaction could also have adverse tax consequences to holders of debt securities or guarantees under other tax laws to which the holders are subject.

Payment of Additional Amounts

Payments made by Aon plc, AGL, AGH, Aon Corporation or a paying agent, as applicable, on the debt securities or in respect to the guarantees will be made free and clear of and without withholding or deduction for or on account of any present or future income, stamp or other tax, duty, levy, impost, assessment or other governmental charge of any nature whatsoever imposed or levied by or on behalf of the government of Ireland, the United Kingdom or, in the case of debt securities issued by Aon plc, AGL or AGH and guaranteed by Aon Corporation, the United States (each, a “Home Country Jurisdiction”), of any territory thereof or by any authority or agency therein or thereof having the power to tax (collectively, “Taxes”), unless Aon plc, AGL, AGH, Aon Corporation or a paying agent is required to withhold or deduct Taxes by law.

If Aon plc, AGL, AGH, Aon Corporation or a paying agent is required to withhold or deduct any amount for or on account of Taxes from any payment made with respect to the debt securities or the guarantees, Aon plc, AGL, AGH or Aon Corporation, as applicable, will pay such additional amounts as may be necessary so that the net amount received by each beneficial owner (including additional amounts) after such withholding or deduction will not be less than the amount the beneficial owner would have received if the Taxes had not been withheld or deducted; provided that no additional amounts will be payable with respect to Taxes:

15

nor shall additional amounts be paid with respect to any payment of the principal of or premium, if any, or interest, if any, on any debt security or any payment in respect of any guarantee to any such holder or beneficial owner who is a fiduciary or a partnership or a beneficial owner who is other than the sole beneficial owner of such payment to the extent a beneficiary or settlor with respect to such fiduciary or a member of such partnership or a beneficial owner would not have been entitled to such additional amounts had it been the holder of the debt security.

All references in this prospectus, other than under “ —Defeasance,” to the payment of the principal of or premium, if any, or interest, if any, on or the net proceeds received on the sale or exchange of, any debt securities or any payment in respect of any guarantee shall be deemed to include additional amounts to the extent that, in that context, additional amounts are, were or would be payable.

The obligations of Aon plc, AGL, AGH and Aon Corporation to pay additional amounts if and when due will survive the termination of the indentures and the payment of all other amounts in respect of the debt securities.

If, as a result of Aon plc’s, AGL’s, AGH’s or Aon Corporation’s consolidation, merger with or conversion into a successor person organized under the laws of a jurisdiction other than Ireland, the United Kingdom or the

16

United States (or, in each case, any political subdivision or taxing authority thereof) as described under “ —Consolidation and Merger,” or the conveyance, transfer or lease by Aon plc, AGL, AGH or Aon Corporation of its assets substantially as an entirety to such successor person, and such an entity expressly assumes the obligations of Aon plc, AGL, AGH or Aon Corporation under the indentures and any outstanding debt securities or guarantees, as applicable, such successor person will pay additional amounts on the same basis as described above, except that references to a “Home Country Jurisdiction” will be treated as references to Ireland, the United Kingdom, the United States and the country in which such successor person is organized or resident (or deemed resident for tax purposes).

Optional Tax Redemption

The issuer may redeem any series of debt securities in whole, but not in part, at its option at any time prior to maturity, upon the giving of not less than 10 nor more than 90 days’ notice of tax redemption to the holders, at a redemption price equal to the principal amount plus accrued and unpaid interest, if any, to the redemption date (except in the case of discounted debt securities, which may be redeemed at the redemption price specified by the terms of each series of such debt securities), if:

17

No notice of any such redemption may be given earlier than 90 days prior to the earliest date on which Aon plc, AGL, AGH, Aon Corporation or such successor person, as applicable, would be obligated to pay any additional amounts.

Aon plc, AGL, AGH, Aon Corporation or such successor person will also pay to each holder, or make available for payment to each such holder, on the redemption date, any additional amounts (as described under “ —Payment of Additional Amounts”) resulting from the payment of such redemption price by it. Prior to the delivery of any notice of redemption, Aon plc, AGL, AGH, Aon Corporation or such successor person will deliver to the trustee an officer’s certificate stating that it is entitled to effect or cause a redemption and setting forth a statement of facts showing that the conditions precedent of the right so to redeem or cause such redemption have occurred, and in the case of a redemption based on an opinion of independent counsel referred to in the second bullet above, such independent counsel’s opinion. Delivery of any notice of redemption will be conclusive and binding on the holders of the securities being redeemed.

Any notice of redemption will be irrevocable once an officer’s certificate has been delivered to the trustee.

Defeasance

Defeasance and Discharge. Unless the debt securities of any series provide otherwise, the issuer and, if applicable, the guarantors may be discharged from any and all obligations in respect of the debt securities of that series and any related guarantee, as applicable (except for certain obligations to register the transfer or exchange of debt securities of that series, to replace stolen, destroyed, lost or mutilated debt securities of that series, to maintain paying agencies, to execute and furnish definitive securities evidenced by temporary securities, to return moneys deposited with or paid to the trustee or any paying agent remaining unclaimed for three years, to compensate and indemnify the applicable trustee or to furnish such trustee (if that trustee is not the registrar) with the names and addresses of holders of debt securities of that series). This discharge, referred to as defeasance, will occur only if, among other things:

That opinion must state that the issuer or, if applicable, the guarantors has or have received from the U.S. Internal Revenue Service a ruling or, since the date of execution of the applicable indenture, there has been a change in the applicable U.S. federal income tax law, in any case, in support of that opinion. (Sections 13.02 and 13.04 of the indentures).

18

In addition, the issuer or, if applicable, the guarantors or the issuer together with the guarantors may also obtain a discharge of either indenture with respect to all debt securities issued under that indenture and any related guarantee, as applicable, by depositing with the applicable trustee, in trust, enough money to pay all amounts due on the debt securities on the date those payments are due or upon redemption of all of those debt securities, so long as those debt securities are by their terms to become due and payable within one year or are to be called for redemption within one year. (Section 12.01 of the indentures).

Defeasance of Certain Covenants and Certain Events of Default. Unless the debt securities of any series provide otherwise, upon compliance with certain conditions:

The conditions include, among other things:

Covenant Defeasance and Certain Other Events of Default. If the issuer or, if applicable, the guarantors or the issuer together with the guarantors exercises or exercise the option to effect a covenant defeasance with respect to the debt securities of any series as described above and the debt securities of that series are thereafter declared due and payable because of an event of default (other than an event of default caused by failing to comply with the covenants that are defeased), the amount of money and securities it has or they have deposited with the applicable trustee would be sufficient to pay amounts due on the debt securities of that series on their respective due dates but may not be sufficient to pay amounts due on the debt securities of that series at the time of acceleration resulting from that event of default. However, the issuer and, if applicable, the guarantors would remain liable for any shortfall.

19

Modification and Waiver

Each indenture provides that the issuer and, if applicable, the guarantors may enter into supplemental indentures with the applicable trustee without the consent of the holders of debt securities to:

The issuer and, if applicable, the guarantors may enter into a supplemental indenture to modify an indenture with the consent of the applicable trustee and the holders of at least a majority in principal amount of outstanding debt securities of each series affected by such supplemental indenture. However, the issuer and, if applicable, the guarantors may not modify an indenture without the consent of the holders of all then-outstanding debt securities of the affected series issued under that indenture to:

The holders of at least a majority in principal amount of the outstanding debt securities of any series may on behalf of the holders of all debt securities of that series waive any past default under the applicable indenture with respect to that series, except a default in the payment of the principal of or any premium or any interest on, any debt security of that series or in respect of a provision which under the applicable indenture cannot be modified or amended without the consent of the holder of each outstanding debt security of that affected series. (Section 6.09 of the indentures).

Global Securities

The debt securities of a series may be issued in whole or in part in the form of one or more global certificates that the issuer will deposit with a depositary identified in an applicable prospectus supplement. Unless and until it is

20

exchanged in whole or in part for the individual debt securities that it represents, a global security may not be transferred except as a whole:

An applicable prospectus supplement will describe the specific terms of the depositary arrangement with respect to a series of debt securities. We anticipate that the following provisions will generally apply to depositary arrangements.

When a global security is issued, the depositary for the global security or its nominee will credit, on its book-entry registration and transfer system, the respective principal amounts of the individual debt securities represented by that global security to the accounts of persons that have accounts with the depositary (“participants”). Those accounts will be designated by the dealers, underwriters or agents with respect to the underlying debt securities or by the issuer if those debt securities are offered and sold directly by the issuer. Ownership of beneficial interests in a global security will be limited to participants or persons that may hold interests through participants. For interests of participants, ownership of beneficial interests in the global security will be shown on records maintained by the applicable depositary or its nominee. For interests of persons other than participants, that ownership information will be shown on the records of participants. Transfer of that ownership will be effected only through those records. The laws of some states require that certain purchasers of securities take physical delivery of securities in definitive form. These limits and laws may impair our ability to transfer beneficial interests in a global security.

As long as the depositary for a global security, or its nominee, is the registered owner of that global security, the depositary or nominee will be considered the sole owner or holder of the debt securities represented by the global security for all purposes under the applicable indenture. Except as provided below, owners of beneficial interests in a global security:

Payments of the principal of, any premium on and any interest on individual debt securities represented by a global security registered in the name of a depositary or its nominee will be made to the depositary or its nominee as the registered owner of the global security representing such debt securities. No issuer, guarantor, trustee, paying agent or registrar for the debt securities will be responsible for any aspect of the records relating to or payments made by the depositary or any participants on account of beneficial interests in the global security.

It is expected that the depositary or its nominee, upon receipt of any payment of principal, any premium or interest relating to a global security representing any series of debt securities, immediately will credit participants’ accounts with the payments. Those payments will be credited in amounts proportional to the respective beneficial interests of the participants in the principal amount of the global security as shown on the records of the depositary or its nominee. It is also expected that payments by participants to owners of beneficial interests in the global security held through those participants will be governed by standing instructions and customary practices. This is now the case with securities held for the accounts of customers registered in “street name.” Those payments will be the sole responsibility of those participants.

If the depositary for a series of debt securities is at any time unwilling, unable or ineligible to continue as depositary and a successor depositary is not appointed within 90 days, the issuer will issue individual debt securities of that series in exchange for the global security or securities representing that series. In addition, the

21

issuer may at any time in its sole discretion determine not to have any debt securities of a series represented by one or more global securities. In that event, the issuer will issue individual debt securities of that series in exchange for the global security or securities. Furthermore, if specified in an applicable prospectus supplement, an owner of a beneficial interest in a global security may, on terms acceptable to the issuer, the trustee and the applicable depositary, receive individual debt securities of that series in exchange for those beneficial interests. The foregoing is subject to any limitations described in an applicable prospectus supplement. In any such instance, the owner of the beneficial interest will be entitled to physical delivery of individual debt securities equal in principal amount to the beneficial interest and to have the debt securities registered in its name. Those individual debt securities will be issued in any authorized denominations.

Guarantees

Under each guarantee, the applicable guarantor will fully and unconditionally guarantee the due and punctual payment of the principal, interest (if any), premium (if any) and all other amounts due on the applicable debt securities and under the indenture when the same shall become due and payable, whether at maturity, pursuant to mandatory or optional redemption or repayments, by acceleration or otherwise, in each case after any applicable grace periods or notice requirements, according to the terms of the applicable debt securities.

The obligations of each guarantor under the guarantees will be full and unconditional, joint and several, regardless of the enforceability of the applicable debt securities, and will not be discharged until all obligations under those debt securities and the applicable indenture are satisfied. Holders of the applicable debt securities may proceed directly against a guarantor under the applicable guarantee if an event of default affecting those debt securities occurs without first proceeding against the issuer.

Conversion Rights

An applicable prospectus supplement will describe the terms and conditions, if any, on which debt securities being offered are convertible into Class A ordinary shares of Aon plc or other securities. Such terms will include the conversion price, the conversion period, provisions as to whether conversion will be at the option of the issuer or the holder, the events requiring an adjustment of the conversion price and provisions affecting conversion in the event of the redemption of such debt securities.

Regarding the Trustee

The issuers have commercial deposits and custodial arrangements with The Bank of New York Mellon Trust Company, N.A. (“BNYM”) and may have borrowed money from BNYM in the normal course of business. The issuers may enter into similar or other banking relationships with BNYM in the future in the normal course of business. In addition, the issuers have provided brokerage and other insurance services in the ordinary course of their respective businesses for BNYM. BNYM may also act as trustee with respect to other debt securities one or both of the issuers have issued.

BNYM will be serving as the trustee under the indentures. Consequently, if an actual or potential event of default occurs with respect to the debt securities, BNYM may be considered to have a conflicting interest for purposes of the Trust Indenture Act. In that case, BNYM may be required to resign under one or more indentures, and the applicable issuer and, if applicable, the applicable guarantor would be required to appoint a successor trustee. For this purpose, a “potential” event of default means an event that would be an event of default if the requirements for giving us default notice or for the default having to exist for a specific period of time were disregarded.

Governing Law

The debt securities, the guarantees and the indentures will be governed by and construed in accordance with the laws of the State of New York.

22

DESCRIPTION OF PREFERENCE SHARES OF AON PLC

In this description, references to “holders” mean those who own preference shares of Aon plc registered in their own names, on the books that the registrar maintains for this purpose, and not those who own beneficial interests in preference shares of Aon plc registered in “street name” or issued in book-entry form and held through one or more depositaries.

The description set forth below is only a summary and is not complete. For more information regarding the preference shares of Aon plc which may be offered by this prospectus, see the documents incorporated by reference in this prospectus, the applicable prospectus supplement, Aon plc’s Constitution (the “Aon plc Constitution”), which is incorporated by reference as an exhibit to the registration statement of which this prospectus forms a part, and any certificate of designations or other instrument establishing a series of preference shares, which will be filed with the SEC as an exhibit to or incorporated by reference in such registration statement at or prior to the time of the issuance of that series of preference shares.

The Aon plc Constitution authorizes Aon plc to issue preference shares, in one or more classes or series, with or without voting rights attached to them, with the number of shares of each class or series and the powers, preferences, rights and limitations thereof (which may include preferences regarding dividends and liquidation rights over the Class A ordinary shares of Aon plc) to be determined by Aon plc’s board of directors at the time of issuance of the relevant preference shares. Aon plc’s board of directors has been authorized to issue up to 50,000,000 preference shares, all of which remain authorized for allotment and issuance. This authority will expire five years from the date of adoption of the Aon plc Constitution (which occurred on March 31, 2020).

We will include the specific terms of each series of the preference shares of Aon plc being offered in an applicable prospectus supplement.

23

DESCRIPTION OF CLASS A ORDINARY SHARES OF AON PLC

In this description, references to “holders” mean those who own Class A ordinary shares of Aon plc registered in their own names, on the books that the registrar we maintains for this purpose, and not those who own beneficial interests in Class A ordinary shares of Aon plc registered in street name or issued in book-entry form and held through one or more depositaries.

The description of the Class A ordinary shares of Aon plc is incorporated in this prospectus by reference to the Current Report on Form 8-K12B filed with the SEC on April 1, 2020. The Class A ordinary shares of Aon plc are listed on the New York Stock Exchange under the symbol “AON.”

For more information regarding the rights attached to the Class A ordinary shares of Aon plc which may be offered by this prospectus, see the applicable prospectus supplement, the Aon plc Constitution, which is incorporated by reference as an exhibit to the registration statement of which this prospectus forms a part, and any other instrument relating to the Class A ordinary shares of Aon plc filed with the SEC as an exhibit to or incorporated by reference in such registration statement at or prior to the time of the issuance of the Class A ordinary shares of Aon plc.

The Aon plc Constitution authorizes Aon plc to allot and issue, and to grant rights to subscribe for or to convert or exchange any security into or for, its Class A ordinary shares, which shall have the same rights, preferences and limitations as its existing Class A ordinary shares. Aon plc’s board of directors has been authorized to issue up to 500,000,000 Class A ordinary shares. Of this amount, as of May 5, 2020, 263,882,994 Class A ordinary shares remained authorized for allotment and issuance. This authority will expire five years from the date of adoption of the Aon plc Constitution (which occurred on March 31, 2020).

24

DESCRIPTION OF SHARE PURCHASE CONTRACTS AND SHARE PURCHASE UNITS OF AON PLC

Aon plc may issue share purchase contracts, representing contracts obligating holders to purchase from Aon plc, and obligating Aon plc to sell to the holders, a specified number of its Class A ordinary shares at a future date or dates. The price per share and the number of Class A Ordinary Shares of Aon plc may be fixed at the time the share purchase contracts are issued or may be determined by reference to a specific formula set forth in the share purchase contracts. The share purchase contracts may be issued separately or as a part of share purchase units consisting of a share purchase contract and, as security for the holder’s obligations to purchase the Class A Ordinary Shares of Aon plc:

Subject to applicable law, the share purchase contracts may require Aon plc to make periodic payments to the holders of the share purchase units or vice versa, and such payments may be unsecured or prefunded on some basis. The share purchase contracts may require holders to secure their obligations in a specified manner and, in certain circumstances, Aon plc may deliver newly issued prepaid share purchase contracts upon release to a holder of any collateral securing such holder’s obligations under the original share purchase contract.

An applicable prospectus supplement will describe the terms of any share purchase contracts or share purchase units and, if applicable, prepaid share purchase contracts.

25