X0508 4 2024-04-29 0000354190 Arthur J. Gallagher & Co. AJG 0001186006 GALLAGHER J PATRICK JR 2850 GOLF ROAD ROLLING MEADOWS IL 60008-4002 1 1 President & CEO 0 Common Stock 2024-04-29 4 M 0 498.17 0 A 163996.1857 D Common Stock 2024-04-29 4 F 0 498.17 232.91 D 163498.0157 D Common Stock 23448 I By Spouse's Trust Common Stock 255965 I By Corporation Common Stock 66703 I By Irrevocable Trust Common Stock 271525 I By Spouse Common Stock 219175 I By Trust Common Stock 367.584 I Gallagher 401(k) plan account Phantom Stock 2024-04-29 4 M 0 498.17 0 D Common Stock 498.17 147177.162 D Shares held in trust for the benefit of my children of which I am sole Trustee. Shares held in revocable trust of which my spouse is sole Trustee and as to which I disclaim beneficial ownership. Held in trust for benefit of children. Each share of phantom stock represents a right to receive one share of Gallagher common stock. These shares represent awards under the Age 62 Plan, a nonqualified deferred compensation plan of the Company, which have been deemed invested in Company common stock at the election of the reporting person. Participants vest in these awards when they attain age 62, or after a one-year period for participants who have attained age 61. The transactions in this report relate solely to the payment of applicable taxes, in accordance with a schedule determined earlier in the year, with respect to a vested award under the Age 62 Plan. /s/ Ryan Session, by power of attorney 2024-05-01