UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): November 29, 2021

Aon plc

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: +353 1 266 6000

Former name or former address, if changed since last report: Not Applicable

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2 below):

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

On November 29, 2021, Aon Corporation, a Delaware corporation (“Aon Corporation”), Aon Global Holdings plc, a public limited company formed under the laws of England and Wales (“AGH” and, together with Aon Corporation, the “Issuers”), Aon plc, an Irish public limited company (“Aon plc”) and Aon Global Limited, a private limited company formed under the laws of England and Wales, and prior to its re-registration, a public limited company formed under the laws of England and Wales named Aon plc (“AGL” and, together with Aon plc, the “Guarantors” and each, a “Guarantor”), entered into an underwriting agreement (the “Underwriting Agreement”) with J.P. Morgan Securities LLC, BofA Securities, Inc. and Goldman Sachs & Co. LLC as representatives of the several underwriters named therein, with respect to the offering and sale by Aon Corporation and AGH of $500,000,000 aggregate principal amount of their 2.600% Senior Notes due 2031 (the “Notes”) under the Registration Statement on Form S-3 (Registration Nos. 333-238189, 333-238189-01, 333-238189-02 and 333-238189-03). Each Guarantor has fully and unconditionally, jointly and severally, guaranteed the Notes pursuant to the Indenture (as defined below) (collectively, the “Guarantees” and, together with the Notes, the “Securities”). The Securities were issued pursuant to an indenture, dated December 3, 2018, as amended and restated on April 1, 2020, as further amended and supplemented by a second supplemental indenture on December 2, 2021 (together, the “Indenture”), among Aon Corporation, AGH, the Guarantors and The Bank of New York Mellon Trust Company, N.A., as trustee (the “Trustee”).

The net proceeds from the offering, after deducting the underwriting discount and estimated offering expenses payable by the Issuers, were approximately $495.4 million. The Issuers intend to use the net proceeds from the offering for general corporate purposes.

The Underwriting Agreement and the Second Indenture Supplement are filed as Exhibits 1.1 and 4.2 to this Current Report on Form 8-K, respectively, and are incorporated by reference herein. The form of the Notes (including the Guarantees) is filed as Exhibit 4.3 to this Current Report on Form 8-K and is incorporated by reference herein.

In connection with the issuance of the Securities, Sidley Austin LLP is filing the legal opinion attached as Exhibit 5.1 to this Current Report on Form 8-K, Freshfields Brukhaus Deringer LLP is filing the legal opinion attached as Exhibit 5.2 and Matheson is filing the legal opinion attached as Exhibit 5.3 to this Current Report on Form 8-K.

(d) Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.