X0306 4 2021-02-08 0000354190 Arthur J. Gallagher & Co. AJG 0001482241 Hudson Scott R 2850 GOLF ROAD ROLLING MEADOWS IL 60008-4002 1 Vice President Common Stock 2021-02-09 4 M 0 6234 46.87 A 41421 D Common Stock 2021-02-09 4 S 0 6234 117.06 D 35187 D Notional Stock Units 2021-02-08 4 A 0 696.8 117.68 A Common Stock 696.8 1786.8 D Non-qualified Stock Option 46.87 2021-02-09 4 M 0 6234 0 D 2021-03-12 Common Stock 6234 416 D The price reported is an average weighted price. The shares were sold in multiple transactions at prices ranging from $117.03 to $117.11. The reporting person will provide to the Securities and Exchange Commission staff, the issuer, or any security holder of the issuer, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. Each notional stock unit represents a right to receive one share of Gallagher common stock. Company match under the Supplemental Savings and Thrift Plan. The notional stock units become payable following the reporting person's separation from service with Gallagher. One-third of this stock option becomes exerciseable on each of the 3rd, 4th, and 5th anniversaries of the grant date. /s/ April Hanes-Dowd, by power of attorney 2021-02-10