2025 Proxy Statement

Dear Fellow Stockholder,

On behalf of our Board of Directors, I invite you to attend our 2025 Annual Meeting of Stockholders. We will be conducting our Annual Meeting virtually again this year. If you are not able to attend, we encourage you to vote by proxy. These proxy materials contain detailed information about the matters on which we are asking you to vote. We hope you will read these materials and then vote in accordance with the Board's recommendations. Your vote is very important to us.

Financial Performance. On a combined basis, our core brokerage and risk management segments produced adjusted revenue1growth of 14.3% (to $11.3 billion) and adjusted EBITDAC1growth of 20.7% (to $3.8 billion). We achieved organic revenue growth of 7.6% in our core brokerage and risk management segments. It was another outstanding year for our franchise, and I am excited about our future.

Acquisition Strategy. We continued to execute on our acquisition strategy in 2024, making significant investments to sustain long-term growth. We completed 48 acquisitions representing $387 million in estimated annualized revenue, adding talent, capabilities and scale across our enterprise. We completed the integration of Willis Re into our global brokerage business. We also signed a definitive agreement to acquire AssuredPartners, a leading U.S.-based insurance broker with client capabilities across commercial property/casualty, specialty, employee benefits and personal lines. The acquisition is subject to regulatory approval, but when it closes, I believe that our combined enterprise will enable us to provide even more value to clients and further position us for future growth.

Board of Directors. Our Board of Directors is comprised of a group of committed and highly qualified individuals who care deeply about our company and bring a diversity of experiences and perspectives to our Board deliberations. In 2024, we added Richard Harries as a director and member of our Audit Committee and Risk and Compliance Committee. Including Mr. Harries, we have added four new independent directors to our Board since 2020, a reflection of our continuing commitment to disciplined board refreshment. Our directors' diverse professional backgrounds, skill sets, independent thought leadership and experience have been invaluable to me and the management team in establishing our long-term business strategy, executing on that strategy and managing both short- and long-term risks facing the company.

1

See Exhibit A for reconciliations of non-GAAP measures.

Commitment to Stockholder Engagement. Our Board values the feedback and insights gained from our engagement with stockholders. During the past year, in addition to our regular discussions with stockholders regarding our financial results, we engaged with stockholders representing more than 50% of shares outstanding on corporate governance, broader sustainability matters and executive compensation. We are committed to including our stockholders' perspectives in our deliberations and we believe that regular communication is necessary in order to ensure thoughtful and informed consideration of evolving best practices in areas of focus for our stockholders.

March 24, 2025

Our Unique Culture. For nearly a century, we have proudly built a reputation of trust and integrity with our clients and colleagues. Now, more than ever, I believe that this culture and history of integrity is a true competitive advantage and a key differentiator when recruiting and retaining talent, attracting acquisition partners, retaining our valued clients and winning new business.

Looking Ahead. We enter 2025 in a position of strength, with industry leading talent, deep expertise, a recognized brand and a consistent global approach to sales and client service. We believe the market environment will remain supportive of growth during 2025. We anticipate clients will add exposures and coverages to their existing insurance programs. In our benefits consulting business, we expect that payrolls will continue to increase and covered lives will remain strong. We see further growth in claim counts within our claims handling business. Additionally, we believe rising loss costs, increased frequency of catastrophe losses and social inflation will lead to increases in property/casualty rates throughout 2025. Our job as brokers and consultants is to help our clients navigate these market dynamics and I am confident our team will continue to deliver outstanding advice and client service in the coming year.

On behalf of our Board of Directors, thank you for your continued support. We look forward to welcoming you at our 2025 Annual Meeting.

Sincerely,

Chairman of the Board and Chief Executive Officer

Arthur J. Gallagher & Co.

2850 Golf Road

Rolling Meadows, Illinois 60008-4050

Notice of 2025 Annual Meeting of Stockholders

Dear Stockholder:

We are pleased to invite you to the 2025 Annual Meeting of Stockholders of Arthur J. Gallagher & Co. (Gallagher or the company), which will be held as a virtual meeting, conducted via live audio webcast, on May 13, 2025, at 9:00 AM CDT. At the meeting, stockholders will vote on each item described below and we will transact such other business that properly comes before the meeting.

Voting Items	Board Recommendations
•Elect each of the 10 nominees named in the accompanying Proxy Statement as directors to hold office until our 2026 Annual Meeting (Item 1)	FOR each nominee
•Ratify the appointment of Ernst & Young LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2025 (Item 2)	FOR
•Approve, on an advisory basis, the compensation of our named executive officers (Item 3)	FOR

Stockholders of record at the close of business on March 17, 2025 are entitled to notice of and to vote at the Annual Meeting. The applicable voting standard and the treatment of abstentions and "broker non-votes" for each of these items are set forth on page 49 of the Proxy Statement. Stockholders may vote shares prior to the meeting by visitingwww.proxyvote.com.

On the day of the Annual Meeting, stockholders of record as of the close of business on March 17, 2025, the record date, are entitled to participate in and vote at the Annual Meeting. To participate in the Annual Meeting, including to vote and ask questions, stockholders of record should go to the meeting website atwww.virtualshareholdermeeting.com/AJG2025, enter the 16-digit control number found on your proxy card or Notice of Internet Availability of Proxy Materials, and follow the instructions on the website. If your shares are held in street name and your voting instruction form or Notice of Internet Availability of Proxy Materials indicates that you may vote those shares through thewww.proxyvote.comwebsite, then you may access, participate in, and vote at the Annual Meeting with the 16-digit access code indicated on that voting instruction form or Notice of Internet Availability of Proxy Materials. Otherwise, stockholders who hold their shares in street name should contact their bank, broker or other nominee (preferably at least 5 days before the Annual Meeting) and obtain a "legal proxy" in order to be able to attend, participate in or vote at the Annual Meeting.

Stockholders are encouraged to log in to the Annual Meeting website before the Annual Meeting begins. Online check-in will be available approximately 10 minutes before the meeting starts. Additional information regarding the rules and procedures for participating in the virtual Annual Meeting will be set forth in our meeting rules of conduct, which stockholders will be able to view during the meeting.

We urge you to read the Proxy Statement for additional information concerning the matters to be considered at the Annual Meeting and then vote in accordance with the Board's recommendations. Your vote is very important to us.

By Order of the Board of Directors

WALTER D. BAY

GENERAL COUNSEL AND SECRETARY March 24, 2025

Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting of Stockholders to Be Held on May 13, 2025:

We are making this Notice of Annual Meeting, this Proxy Statement, our 2024 Annual Report, and the Notice of Internet Availability of Proxy Materials available on the Internet atwww.materials.proxyvote.com/363576and mailing copies of these proxy materials to certain stockholders on or about March 24, 2025.

Proxy Statement Table of Contents

Corporate Governance1

Item 1- Election of Directors.......................................................1

FREQUENTLY REFERENCED

Key Governance Practices...........................................................8

TOPICS

Board Leadership Structure.........................................................Director Independence.................................................................Compensation Committee Interlocks and

8

9

Insider Participation......................................................................Stockholder Views........................................................................Board's Role in Risk Oversight.....................................................Sustainability Oversight and Activities..........................................Other Board Matters.....................................................................Director Compensation.................................................................Certain Relationships and Related Person Transactions.............Security Ownership by Certain Beneficial Owners and Management.................................................................................Equity Compensation Plan Information........................................

9

Director Qualifications

2

9

9

12

13

Board Skills and Experience

2

14

15 16 18

Key Governance Practices

8

Audit Matters

19

Board's Role in Risk Oversight

9

Item 2- Ratification of Appointment of Independent Auditor.......Audit Committee Report...............................................................

19

20

Sustainability Oversight and

12

Executive Compensation

21

Activities

Compensation Discussion and Analysis......................................Overview of Our Executive Compensation Program....................2024 Compensation.....................................................................Compensation Decision-Making Process.....................................Comparative Market Assessment.................................................Compensation Committee Report................................................Executive Compensation Tables..................................................Item 3- Advisory Vote to Approve the Compensation of Our Named Executive Officers...........................................................Pay versus Performance..............................................................CEO Pay Ratio.............................................................................

21

22

24

30

Compensation Discussion and Analysis

21

31

32

Questions and Answers About the Annual Meeting..................

33 43 44 48 49

Key Executive Compensation Practices

23

2024 Summary Compensation Table

33

Exhibits

A-1

Exhibit A: Information Regarding Non-GAAP Measures..............Exhibit B: Resources....................................................................

A-1

B-1

Some of the statements in this proxy statement, including those related to our interim goal of 50% reduction in consolidated Scope 1 and Scope 2 carbon emissions on a per-employee basis by 2030 in addition to our goal of achieving operational net zero carbon emissions (Scope 1 and Scope 2) by 2050, may be considered forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995. We caution investors that these forward-looking statements are not guarantees of future performance, and are subject to certain risks and uncertainties that could cause actual results to differ materially. Factors that could cause our future performance and actual results or outcomes to differ, possibly materially, from those expressed in the forward-looking statements include, but are not limited to, our ability to formulate and implement plans to reduce our Scope 1 and 2 carbon emissions as anticipated; our reliance on third parties, whose actions are outside our control; and the lack of widely accepted standards for measuring carbon emissions associated with insurance and reinsurance brokerage, consulting and claims managements activities, as well as other factors discussed in our 2024 Annual Report on Form 10-K, subsequent Quarterly Reports on Forms 10-Q, and the other filings we make with the Securities and Exchange Commission. Accordingly, you should not place undue reliance on forward-looking statements, which speak only as of, and are based on information available to us on, the date of the applicable document. We do not undertake any obligation to update any forward-looking statements made in or release publicly any revisions to these forward-looking statements to reflect events or circumstances after the date of this proxy statement, which speaks as of the date issued, or to reflect newinformation, future or unexpected events or otherwise, except as required by applicable law or regulation. The inclusion of forward-looking and other sustainability-related statements in this proxy statement is not an indication that these contents are necessarily material to investors or required to be disclosed in our filings with the SEC. In addition, historical, current and forward-looking sustainability-related statements may be used based on standards for measuring progress that are still developing, internal controls and processes that continue to evolve, and assumptions that are subject to change in the future.

M

Corporate Governance

ITEM 1 - Election of Directors

Evaluation Process for Director Candidates

The Nominating/Governance Committee considers director candidates suggested by stockholders, management or other members of the Board of Directors (Board) and may hire consultants or search firms to help identify and evaluate potential director candidates. In some cases, nominees have been individuals known to Board members or others. In the case of Richard Harries, a member of senior management initially identified him as a potential director nominee. Prior to his nomination, Mr. Harries met separately with the Chairman and CEO and each member of the Nominating/Governance Committee (which includes our Independent Lead Director), who considered his candidacy. After review and discussion, the Nominating/Governance Committee recommended, and the Board approved, Mr. Harries's appointment to the Board. For information regarding how stockholders can submit a director candidate for consideration by the Nominating/Governance Committee, as well as for information regarding "proxy access," see page 51.

The Nominating/Governance Committee evaluates director candidates by considering their judgment, qualifications, attributes, skills, integrity, gender, racial/ethnic diversity, international business or other experience relevant to our global activities and other factors it deems appropriate. The Committee looks for candidates who are leaders in the organizations with which they are affiliated and have experience in positions with a high degree of responsibility. The Committee seeks candidates free from relationships or conflicts of interest that could interfere with the director's duties to Gallagher or our stockholders. The Committee also evaluates candidates' independence and takes into account applicable requirements under Securities and Exchange Commission (SEC) rules and New York Stock Exchange (NYSE) listing standards.

Board Diversity

Our Board nominees reflect diversity of professional background, experiences, viewpoints, gender, race/ethnicity, tenure, nationality and age. Our Board has adopted the "Rooney Rule" for director searches. Under this policy, our Governance Guidelines provide that, when recruiting director candidates, the Nominating/Governance Committee endeavors to include qualified diverse candidates, and requests that any search firm it engages endeavor to do the same, including women and racially/ethnically diverse persons to expand the pool from which new director nominees are ultimately chosen based on merit. The Committee actively seeks Board members from diverse backgrounds who combine a broad spectrum of experience and expertise with a reputation for integrity. The Committee assesses the effectiveness of the Board's diversity search policy as part of its annual review process.

These percentages include our Chairman and CEO, Pat Gallagher.

Board Nominees and Vote Required

Upon the recommendation of the Nominating/Governance Committee, the Board has nominated our Chairman and Chief Executive Officer (CEO) and each of the additional nine individuals listed below to hold office until the next annual meeting and the election and qualification of their successors or, if earlier, until their resignation, death or removal. Each of the nominees currently serves on the Board and, except for Mr. Harries who was appointed in July 2024, was last elected at the 2024 annual meeting, and all of the nominees have consented to serve on the Board if elected. If any nominee should become unable or unwilling to serve, the Board may nominate another person to stand for election or reduce the size of the Board.

Each director nominee who receives more "FOR" votes than "AGAINST" votes at the Annual Meeting will be elected. Abstentions will have the same effect as a vote "AGAINST." Any incumbent director nominee who receives a greater number of votes

"AGAINST" election than votes "FOR" election is required to tender an offer of resignation for consideration by the Nominating/Governance Committee in accordance with our Governance Guidelines.

Director Qualifications

We have summarized below the key qualifications and areas of experience that led our Board to conclude that each non-management director nominee is qualified to serve on our Board; however, this is not intended to be an exhaustive list of their qualifications or contributions to our Board.

Non-Management Director Nominees

CEO / COO Experience

Finance / Capital Markets

Change Management

Risk Management / Governance

Sales and

MarketingInternationalInsurance Industry

Independence

Sherry Barrat

X

X

X

X

X

X

X

Deborah Caplan

X

X

X

X

X

Teresa Clarke

X

X

X

X

X

X

John Coldman

X

X

X

X

Richard Harries

X

X

X

X

X

X

David Johnson

(Lead Independent Director)

X

X

X

X

X

X

Chris Miskel

X

X

X

X

X

X

Ralph Nicoletti

X

X

X

X

Norman Rosenthal

X

X

X

X

The Board recommends that you vote "FOR" the election of each of the director nominees listed below

SHERRY BARRAT

Ms. Barrat's qualifications to serve on our Board and chair our Compensation Committee include her executive management, operational and financial experience, in particular her deep understanding of the financial services industry and her experience leading a global client service and sales organization. Her roles at NortheTrust, NextEra Energy and Prudential Insurance mutual funds have given her experience navigating complex and changing regulatory environments. She also has significant experience with change management, including planning and implementing a CEO succession plan as part of NextEra Energy's board.

Career Highlights

• •NortheTrust Corporation (1990-2012)

  Global financial holding company

  • oVice Chairman

  • oPresident, Personal Financial Services

  • oMember, Management Committee

Previous Public Company Boards

• •NextEra Energy, Inc. (1998-2024)

  • oLead Director

  • oExecutive Committee

  • oCompensation Committee

  • oGovernance & Nominating Committee

• •Prudential Insurance mutual funds (2013-2024)

  • oIndependent trustee or director of various funds

  • oVice Chair, Investment Review Committee

  • oGovernance & Nominating Committee

  • oCompliance Committee

DEBORAH CAPLAN

Ms. Caplan's qualifications to serve on our Board include her senior executive experience, a history of building corporate cultures founded on strong values and her extensive operational experience. Her senior executive roles at NextEra Energy, one of the largest electric power and energy infrastructure companies in North America and a leader in the renewable energy industry, have given her valuable experience navigating a complex regulatory environment and the risks and opportunities presented by climate change. In addition, her experience as a human resources leader and member of other public company boards enable her to contribute to sound corporate governance and executive compensation practices at the company.

Career Highlights

• •NextEra Energy, Inc. (2005-2024)

  Electric power and clean energy company

  • oExecutive Vice President, Human Resources and Corporate Services (2013-2024)

  • oVice President and Chief Operating Officer, Florida Power & Light Company

    (2011-2013)

  • oVice President of Integrated Supply Chain (2005-2011)

• •General Electric Company (prior to 2005)

  Global conglomerate

  • oSenior Vice President of Global Operations for Vendor Financial Services, GE Capital

  • oOther senior roles in manufacturing and product development, GE Aircraft Engines

Current Public Company Boards

• •Valmont Industries, Inc. (2024-present)

  • oHuman Resources Committee

• •Mid-America Apartment Communities, Inc. (2023-present)

  • oCompensation Committee (Chair)

  • oNominating & Corporate Governance Committee

Previous Public Company Boards

• •Terminix Global Holdings, Inc. (2019-2022)

  • oChair, Compensation Committee

  • oEnvironmental, Health and Safety Committee

Director since:2021

Committee Memberships:

• •Audit

• •Risk and Compliance

Public Company Boards:2

Independent

TERESA CLARKE

Ms. Clarke's qualifications to serve on our Board include her extensive international and financial services expertise, particularly in the areas of corporate finance and mergers & acquisitions. In addition, her roles leading or overseeing technology companies have given her valuable experience in change management, including navigating changing regulatory environments and pivoting businesses to take advantage of new technologies.

Career Highlights

• •Africa.com LLC (2010-present)

  Africa-related digital media content company

  • oChair and Chief Executive Officer

• •Goldman Sachs & Co. (Prior to 2010)

  Global financial services firm

  • oManaging Director, Investment Banking

Current Public Company Boards

• •American Tower Corporation (2021-present)

  • oAudit Committee

Previous Public Company Boards

• •Change Financial Limited (2016-2020) - Australian Stock Exchange

  • oBoard Chair

  • oAudit Committee

• •Cim Group Ltd (2016-2020) - Mauritius Stock Exchange

  • oCorporate Governance Committee

Community Involvement

• •Smithsonian National Museum of African Art (2022-present)

  • oChair, Advisory Board

JOHN COLDMAN, OBE

Mr. Coldman's qualifications to serve on our Board include his international insurance industry knowledge, his experience within the Lloyd's and London marketplaces, his experience with public company matters and mergers and acquisitions and his significant expertise in reinsurance.

Career Highlights

• •The Benfield Group (1988-2008)

  Reinsurance and risk intermediary company

  • oChairman

  • oManaging Director

Previous Public Company Boards

• •Omega Insurance Holdings Limited (2010-2012) - London Stock Exchange

  • oChairman

• •Brit PLC (1996-2000) - London Stock Exchange

  • oChairman

Other Board Experience

• •Lloyd's of London (2001-2006)

  • oDeputy Chairman

  • oMember of Council

• •Roodlane Medical Ltd. (2007-2011)

  • oNon-Executive Chairman

Community Involvement

• •A U.K. citizen, Mr. Coldman was appointed an Officer of the Order of the British Empire (OBE) in the Queen's Birthday Honours List 2017, for "services to business, young people, and charity."

PAT GALLAGHER

Mr. Gallagher is the only member of management serving on the Board. His 51 years of experience with our company and 39 years of service on the Board, his deep knowledge of our company and the insurance industry and his extensive leadership experience greatly enhance the Board's decision making and enable Mr. Gallagher to serve as a highly effective Chairman of the Board.

Career Highlights

• •Arthur J. Gallagher & Co. (1974-present)

  • oChairman

  • oChief Executive Officer

  • oPresident and Chief Operating Officer

  • oVice President of Operations

  • oProduction Account Executive

Previous Public Company Boards

• •InnerWorkings, Inc. (2011-2019)

  • oCompensation Committee

  • oNominating/Governance Committee

Insurance Industry Affiliations

• •The Institutes, previously known as American Institute for Chartered Property Casualty Underwriters (2003-present)

  • oBoard of Trustees

Community Involvement

• •Mr. Gallagher was granted Freedom of the City of London in 2007 by the city's Lord Mayor in recognition of his outstanding contribution to the Lloyd's insurance market and for his support of the Gallagher Lifelong Learning scholarships.

RICHARD HARRIES

Mr. Harries' qualifications to serve on our Board include over 35 years of insurance industry experience in the UK and other highly regulated markets and his experience growing businesses as an operational leader. His roles at Atrium Underwriters Limited provided him with significant experience in mergers & acquisitions and change management, including with respect to technology initiatives.

Career Highlights

• •Atrium Underwriters Limited (1997-2023)

  Lloyd's managing agent and syndicate

  • oChief Executive Officer and Director

  • oChief Underwriter Officer

  • oEnergy Underwriter

• •Willis Faber & Dumas (1987-1997)

  Director since:2024

  Insurance broker

  • oExecutive Director, Head of International Energy

    Committee Memberships:

  • oOther senior roles in the energy sector

• •Audit

• •Risk and Compliance

Other Board Experience

Public Company Boards:1

• •Lloyd's Market Association (2014-2022)

• •London Market Group (2020-2022)

  Independent

  • oTarget Operating Module Oversight Board

Director since:2003

Committee Memberships:

• •Compensation

• •Nominating/Governance

• •Risk and Compliance

Public Company Boards:1

Independent Lead Director since 2016

DAVID JOHNSON

Mr. Johnson's qualifications to serve on our Board and as Independent Lead Director include his knowledge of corporate governance and executive compensation best practices and his experience as a senior executive of global businesses. These roles have provided him with significant experience in change management and navigating complex regulatory environments.

Career Highlights

• •Aryzta AG, now Aspire Bakeries (2018-2021)

  Global food business

  • oNon-Executive Chairman, North America

  • oChief Executive Officer, North America

• •Barry Callebaut AG (2009-2017)

  Cocoa and chocolate products manufacturer

  • oPresident and Chief Executive Officer, Americas

  • oMember, Global Executive Committee

• •Michael Foods, Inc. (2007-2009)

  Food processor and distributor

  • oPresident, Chief Executive Officer and Board Member

  • oChief Operating Officer

• •Kraft Foods Global, Inc. (prior to 2007)

  Global food and beverage company

  • oPresident, Kraft Foods North America

  • oMember, Management Committee

  • oOther senior roles in marketing, strategy, operations, procurement and general management

Other Board Experience

• •Mosaic Flavors (2022-present)

• •Jacobs Holding AG (2018-2021)

  • oBoard of Advisors

• •Michael Foods, Inc. (2008-2009)

CHRIS MISKEL

Mr. Miskel's qualifications to serve on our Board and chair our Nominating/Governance Committee include his senior executive experience, his involvement in setting strategy for large businesses such as Lilly, Baxter, Baxalta and Shire, his extensive sales and marketing experience, and his knowledge of the healthcare industry and related privacy and cybersecurity issues. His senior roles in the pharmaceutical industry have also provided him with experience navigating complex and changing regulatory environments.

Career Highlights

• •Versiti, Inc. (2017-present)

  Blood products supply company

  • oPresident and Chief Executive Officer

• •Baxter / Baxalta / Shire (2013-2017) - Baxalta Incorporated spun off from Baxter International Inc. in 2015 and was acquired by Shire plc in 2016

  Global healthcare and pharmaceutical companies

  • oHead of Immunology (2015-2017)

  • oVice President, Plasma Strategy and New Products, Global BioTherapeutics

    (2014-2015)

  • oVice President, U.S. BioScience National Accounts (2013-2014)

• •Eli Lilly and Company (prior to 2013)

  Pharmaceutical company

  • oGeneral Manager, Lilly Australia and New Zealand

  • oOther senior roles

Community Involvement

• •Butler University (2021-present)

  • oBoard of Trustees

• •Medical College of Wisconsin (2018-present)

  • oBoard of Directors

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Disclaimer

Arthur J.Gallagher & Co. published this content on March 25, 2025, and is solely responsible for the information contained therein. Distributed by Public, unedited and unaltered, on March 25, 2025 at 14:08:49.030.