AJG Arthur J Gallagher and Company

$1,000,000,000

$500,000,000 5.450% Senior Notes due 2034 (the “2034 Notes”)

$500,000,000 5.750% Senior Notes due 2054 (the “2054 Notes”)

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*Ratings may be changed, suspended or withdrawn at any time and are not a recommendation to buy, hold or sell any security.

The issuer has filed a registration statement (including a prospectus and a preliminary prospectus supplement) with the Securities and Exchange Commission for the offering to which this communication relates. Before you invest, you should read the prospectus and the preliminary prospectus supplement in that registration statement and other documents the issuer has filed with the Securities and Exchange Commission for more complete information about the issuer and this offering. You may get these documents for free by visiting EDGAR on the Securities and Exchange Commission’s website at www.sec.gov. Alternatively, the issuer, any underwriter or any dealer participating in the offering will arrange to send you the prospectus and preliminary prospectus supplement if you request it by calling BofA Securities, Inc. at 1-800-294-1322 or J.P. Morgan Securities LLC at 1-212-834-4533.

We expect that delivery of the Notes will be made against payment therefor on or about the closing date specified in this communication, which will be the third business day following the Trade Date (this settlement cycle being referred to as “T+3”). Under Rule 15c6-1 of the Securities Exchange Act of 1934, as amended, trades in the secondary market generally are required to settle in two business days, unless the parties to any such trade expressly agree otherwise. Accordingly, investors who wish to trade the Notes on the Trade Date, by virtue of the fact that the Notes initially will settle T+3, should specify an alternative settlement arrangements at the time of any such trade to prevent a failed settlement. Purchasers of Notes who wish to trade the Notes on the Trade Date should consult their own advisors.

ANY DISCLAIMERS OR OTHER NOTICES THAT MAY APPEAR BELOW ARE NOT APPLICABLE TO THIS COMMUNICATION AND SHOULD BE DISREGARDED. SUCH DISCLAIMERS OR OTHER NOTICES WERE AUTOMATICALLY GENERATED AS A RESULT OF THIS COMMUNICATION BEING SENT VIA BLOOMBERG OR ANOTHER E-MAIL SYSTEM.

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