AJG · Arthur J. Gallagher & Co. · Insider Trading

This transaction represents a gift from the reporting person's father to an irrevocable trust of which the reporting person and his siblings are beneficiaries, and the reporting person is the acting trustee. The reporting person disclaims beneficial ownership of the shares held by the trust except to the extent of his pecuniary interest therein.

Shares held in trust for the benefit of the reporting person and immediate family members, of which he and his immediate family members, as applicable, is a trustee.

This transaction represents a gift for estate planning purposes.

The price reported is an average weighted price. The shares were sold in multiple transactions on 9/2/2026 at prices ranging from $263.894 to $264.15. 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 ranges set forth in the footnotes to this Form 4.

One-third of this stock option becomes exerciseable on each of the 3rd, 4th, and 5th anniversaries of the grant date.

This acquisition resulted from the reporting person's election in a prior year (pursuant to the Company's Director Deferral Plan) to defer the reporting person's annual cash retainer, which the Company pays on a quarterly basis, into deferred share units that will be distributed in the form of the Company's common stock.

The price reported is an average weighted price. The shares were sold in multiple transactions on 8/24/2026 at prices ranging from $270.01 to $270.17. 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.

One-third of this stock option becomes exerciseable on each of the 3rd, 4th, and 5th anniversaries of the grant date.

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.

This transaction represents a gift for estate planning purposes from the reporting person's spouse to an irrevocable trust of which the reporting person and his children are beneficiaries. The reporting person disclaims beneficial ownership of the shares held by the trust except to the extent of his pecuniary interest therein.

Shares held in a revocable trust and an irrevocable trust of which the reporting person's spouse is sole Trustee and as to which he disclaims beneficial ownership

Each notional stock unit represents a right to receive one share of Gallagher common stock.

The notional stock units become payable in July 2026 and following the reporting person's separation from service with Gallagher.

Each notional stock unit represents a right to receive one share of Gallagher common stock.

Portions of these notional stock units are payable to the reporting person in shares of common stock in July of 2026, 2027 and 2028 and following the reporting person's separation from service.

Portions of these notional stock units are payable to the reporting person in shares of common stock in July of 2026, 2027 and 2028 and following the reporting person's separation from service.

Each notional stock unit represents a right to receive one share of Gallagher common stock.

Portions of these notional stock units are payable to the reporting person in shares of common stock in July of 2026 and following the reporting person's separation from service.

Each notional stock unit represents a right to receive one share of Gallagher common stock.

This disposition of notional stock units is a discretionary transaction by the reporting person to move assets he holds in the company's Supplemental Savings and Thrift Plan ("SS&T Plan"), a nonqualified deferred compensation plan, from the investment option representing Gallagher common stock to cash partially to cover his expected tax obligations as a result of a distribution that will occur in July 2026 under such plan.

Portions of these notional stock units are payable to the reporting person in shares of common stock in July of 2026, 2028 and 2029 and following the reporting person's separation from service.

The reporting person's disposition of Gallagher common stock reported herein was matchable under Section 16(b) of the Securities and Exchange Act of 1934, to the extent of 12,892.211 shares the reporting person invested in through the SS&T Plan on February 12, 2026. The reporting person had a loss of approximately $32,123 in connection with this short-swing transaction.

This acquisition resulted from the reporting person's election in a prior year (pursuant to the Company's Director Deferral Plan) to defer the reporting person's annual cash retainer, which the Company pays on a quarterly basis, into deferred share units that will be distributed in the form of the Company's common stock.

This acquisition resulted from the reporting person's election in a prior year (pursuant to the Company's Director Deferral Plan) to defer the reporting person's annual cash retainer, which the Company pays on a quarterly basis, into deferred share units that will be distributed in the form of the Company's common stock.

Shares held in trust for the benefit of the reporting person and immediate family members, of which he and his immediate family members, as applicable, is a trustee.

Restricted stock unit award vesting on the earlier of one year after the date of grant or the reporting person's departure from the Board.

Restricted stock unit award vesting on the earlier of one year after the date of grant or the reporting person's departure from the Board.

Restricted stock unit award vesting on the earlier of one year after the date of grant or the reporting person's departure from the Board.

Restricted stock unit award vesting on the earlier of one year after the date of grant or the reporting person's departure from the Board.

Restricted stock unit award vesting on the earlier of one year after the date of grant or the reporting person's departure from the Board.

Restricted stock unit award vesting on the earlier of one year after the date of grant or the reporting person's departure from the Board.

Restricted stock unit award vesting on the earlier of one year after the date of grant or the reporting person's departure from the Board.

Restricted stock unit award vesting on the earlier of one year after the date of grant or the reporting person's departure from the Board.

The transactions in this report relate solely to the distribution of vested shares under the Age 62 Plan and the withholding of shares to cover applicable income and employment taxes.

The transactions in this report relate solely to the distribution of vested shares under the Age 62 Plan and the withholding of shares to cover applicable income and employment taxes.

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.

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.

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 distribution of vested shares under the Age 62 Plan and the withholding of shares to cover applicable income and employment taxes.

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 in the year they attain age 62, or after a one-year period for participants who have attained age 61.