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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-K

For the fiscal year ended December 31, 2025

For the transition period from__________________to

Commission file number 1-09761

ARTHUR J. GALLAGHER & CO.

(Exact name of registrant as specified in its charter)

(630) 773-3800

(Registrant’s telephone number, including area code)

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes x No o.

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes o No x.

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes x No o.

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T during the preceding 12 months (or for such shorter period that the registrant was required to submit such files). Yes x No o.

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or emerging growth company. See definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b‑2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 726(b)) by the registered public accounting firm that prepared or issued its audit report Yes x No o.

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements. o

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). o

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes o No x.

The aggregate market value of the voting common equity held by non-affiliates of the registrant, computed by reference to the last reported price at which the registrant’s common equity was sold on June 30, 2025 (the last day of the registrant’s most recently completed second quarter) was $71,117 million.

The number of outstanding shares of the registrant’s Common Stock, $1.00 par value, as of January 31, 2026 was 257.1 million.

Documents incorporated by reference: Portions of Arthur J. Gallagher & Co.’s definitive 2026 Proxy Statement are incorporated by reference into this Form 10‑K in response to Part III to the extent described herein.

Information Concerning Forward-Looking Statements

This report contains certain statements related to future results, or states our intentions, beliefs and expectations or predictions for the future of Arthur J. Gallagher & Co. and its subsidiaries, collectively referred to herein as we, our, us, Gallagher or the Company, which are forward-looking statements as that term is defined in the Private Securities Litigation Reform Act of 1995. Forward‑looking statements relate to expectations or forecasts of future events. Such statements use words such as “anticipate,” “believe,” “estimate,” “expect,” “contemplate,” “forecast,” “project,” “intend,” “plan,” “potential,” and other similar terms, and future or conditional tense verbs like “could,” “may,” “might,” “see,” “should,” “will” and “would.” You can also identify forward-looking statements by the fact that they do not relate strictly to historical or current facts. For example, we may use forward-looking statements when addressing topics such as: the impact of general economic conditions, including inflation, interest rates and market uncertainty; the effects of geopolitical volatility, including repercussions from the armed conflicts in Ukraine, the Middle East, Latin America and the Caribbean; market and industry conditions, including competitive and pricing trends and the impact of large natural events; acquisition strategy including the expected size of our acquisition program; the expected impact of acquisitions and dispositions and integrating recent acquisitions, including comments regarding the expected benefits of our acquisition of Woodruff-Sawyer & Co. (which we refer to as Woodruff Sawyer) and Dolphin TopCo, Inc., the holding company of AssuredPartners, Inc. (which we refer to as AssuredPartners), and other acquisitions larger than our typical tuck-in acquisitions and the expected duration and costs of integrating such large acquisitions; the development and performance of our services and products; changes in the composition or level of our revenues or earnings; our cost structure and the size and outcome of cost-saving or restructuring initiatives; future capital expenditures; future debt levels and anticipated actions to be taken in connection with maturing debt; future debt to earnings ratios; the outcome of contingencies; dividend policy; pension obligations; cash flow and liquidity; capital structure and financial losses; future actions by regulators; the outcome of existing regulatory actions, audits, reviews or litigation; the impact of changes in accounting rules; financial markets; interest rates; foreign exchange rates; matters relating to our operations; income taxes; expectations regarding our investments; human capital management, including diversity and inclusion initiatives, and sustainability, including climate-resilience and climate-advisory products and services and our carbon emissions. These forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from either historical or anticipated results depending on a variety of factors.

Potential factors that could impact results include:

• Global economic and geopolitical events, such as fluctuations in interest and inflation rates; geo-economic fragmentation and protectionism such as tariffs, trade wars or similar governmental actions affecting the flows of goods, services or currency; a recession or economic downturn; a U.S. government shutdown; political violence and instability, including as a result of the armed conflicts in Ukraine, the Middle East, Latin America and the Caribbean;

• Economic conditions that result in financial difficulties for underwriting enterprises or lead to reduced risk-taking capital capacity, for example, as a result of large payouts related to extreme weather events, or to the failure of such enterprises, including the increased risk of errors and omissions (which we refer to as E&O) claims against us;

• Risks that could negatively affect the success of our acquisition strategy, including the impact of economic uncertainty on our ability to source, review and price acquisitions, continuing consolidation in our industry and interest in acquiring insurance brokers on the part of private equity firms and newly public insurance brokers, which makes it more difficult to identify targets and in some cases makes them more expensive, inaccurate assumptions and failure to realize expected benefits; the risk that we may not receive timely regulatory approval of pending transactions, closing risks; execution risks, integration risks, poor cultural fit, the risk of post-acquisition deterioration leading to intangible asset impairment charges, and the risk we could incur or assume unanticipated liabilities such as cybersecurity issues or violations of anti‑corruption and sanctions laws;

• Risks related to Woodruff Sawyer, AssuredPartners and other acquisitions larger than our usual tuck-in acquisitions, including risks related to our ability to successfully integrate operations, the possibility that our assumptions may be inaccurate resulting in unforeseen obligations or liabilities and failure to realize the expected benefits of these acquisitions;

• Damage to our reputation, including as a result of failing to uphold our culture and the potential for the Internet and social media to magnify the effects of such reputational issues;

• Failure to meet our sustainability aspirations, goals and initiatives or to comply with increasingly complex climate-related and other sustainability regulations, heightened scrutiny, including a growing backlash against sustainability initiatives, and increased risks related to “greenwashing” and “greenhushing;”

• Failure to apply technology, data analytics and artificial intelligence (which we refer to as AI) effectively in driving value for our clients through technology-based solutions, or failure to gain internal efficiencies and effective internal controls through the application of technology and related tools;

• Risks associated with the use of AI in our business operations, including regulatory, data privacy, cybersecurity, E&O, intellectual property and competition risks;

• Failure to attract and retain experienced and qualified talent, including our senior management team, or adequately plan and execute for the succession of such leaders; increased costs resulting from increased compensation and benefits packages as a result of a tighter labor market, and negative effects from restrictions on non-compete agreements at the state level;

• A disaster or other significant disruption to business continuity for our own operations or those of third-parties on which we rely, including cybersecurity incidents; natural disasters; political violence and unrest in the U.S. or elsewhere around the world; for example, our substantial operations in India could be negatively impacted as a result of the dispute between India and Pakistan involving the Kashmir region, rising tensions between India and China, or incidents of terrorism in India, civil unrest or other reasons;

• Sustained increases in the cost of employee benefits and compensation expense;

• Risks arising from our international operations and changes in international conditions, including the risks posed by political and economic uncertainty in certain countries (including repercussions from the armed conflicts in Ukraine, the Middle East, Latin America and the Caribbean), maintaining regulatory and legal compliance across multiple jurisdictions (such as those relating to violations of anti‑corruption, sanctions, and privacy laws, increasingly complex regulatory requirements related to climate change and sustainability issues); increased protectionism, tariffs, and trade wars, climate change and other long-term sustainability matters, increased scrutiny of the use of off-shore centers of excellence such as those we operate and global health risks;

• Risks related to changes in U.S. or foreign tax laws, including a U.S. or foreign tax rate change, such as those resulting from the One Big Beautiful Bill Act (which we refer to as OBBBA), changes to the U.S. Inflation Reduction Act, the Organisation for Economic Co-operation and Development’s (which we refer to as the OECD) global minimum corporate tax regime, and other local policy changes;

• Competitive pressures, including as a result of innovation, in each of our businesses;

• Volatility or declines in premiums or other adverse trends in the insurance industry;

• The higher level of variability inherent in contingent and supplemental revenues versus standard commission revenues;

• Risks particular to our benefit consulting operations, including risks related to the acquisition of BCHR Holdings, L.P. and its subsidiaries, dba Buck (which we refer to as Buck) and Redington Ltd. (which we refer to as Redington), an investment consulting firm regulated by the Financial Conduct Authority (which we refer to as the FCA);

• Risks particular to our third-party claims administrations operations, including risks related to the availability of RISX‑FACS®, our proprietary risk management information system, wage inflation, staffing shortages, any slowing of the trend toward outsourcing claims administration, and the concentration of large amounts of revenue with certain clients;

• Climate risks, including the risk of a systemic economic crisis and disruptions to our business caused by the transition to a low-carbon economy;

• Cyber-attacks or other cybersecurity incidents and the heightened risk of such attacks as a result of the armed conflicts in Ukraine, the Middle East, Latin America and the Caribbean, improper disclosure of confidential, personal or proprietary data and changes to laws and regulations governing cybersecurity and data privacy;

• Unfavorable determinations related to contingencies and legal proceedings, including; violations or alleged violations of the U.S. Foreign Corrupt Practices Act (which we refer to as FCPA), the U.K. Bribery Act 2010 or other anti-corruption laws and the Foreign Account Tax Compliance provisions of the Hiring Incentives to Restore Employment Act, and the outcome of any existing or future investigation, review, regulatory action or litigation;

• Failure to comply with regulatory requirements, including those related to governance and control requirements in particular jurisdictions, international sanctions, including new sanctions laws as a result of the armed conflicts in Ukraine, the Middle East, Latin America and the Caribbean; laws relating to the disclosure of sustainability matters; laws relating to the use of AI, or a change in regulations or enforcement policies that adversely affects our operations (for example, relating to insurance broker compensation methods or restrictions on non-compete agreements);

• Changes to our financial presentation from new accounting estimates and assumptions;

• Intellectual property risks;

• Risks related to our legacy clean energy investments, including intellectual property claims, environmental and product liability claims, environmental compliance costs and the risk of disallowance by the Internal Revenue Service of previously claimed tax credits;

• The risk that our outstanding debt adversely affects our financial flexibility and restrictions and limitations in the agreements and instruments governing our debt;

• The risk of credit rating downgrades;

• The risk that we may not be able to receive dividends or other distributions from our subsidiaries, including the effects of significant changes in foreign exchange rates;

• The risk of share ownership dilution when we issue common stock; and

• Volatility of the price of our common stock.

Forward-looking statements are not guarantees of future performance. They involve risks, uncertainties and assumptions, including the risk factors referred to above. Our future performance and actual results or outcomes may differ materially from those expressed in forward-looking statements. 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. Many of the factors that will determine these results are beyond our ability to control or predict. All subsequent written and oral forward-looking statements attributable to us or any person acting on our behalf are expressly qualified in their entirety by the cautionary statements contained or referred to in this section. Forward-looking statements speak only as of the date that they are made, and we do not undertake any obligation to update any such statements or release publicly any revisions to these forward-looking statements to reflect events or circumstances after the date of this report or to reflect new information, future or unexpected events or otherwise, except as required by applicable law or regulation. In addition, historical, current and forward-looking sustainability-related statements may be 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.

A detailed discussion of the factors that could cause actual results to differ materially from our published expectations is contained under the heading “Risk Factors” in our filings with the Securities and Exchange Commission (SEC), including this report and any other reports we file with the SEC in the future.

Arthur J. Gallagher & Co.

Annual Report on Form 10-K

For the Fiscal Year Ended December 31, 2025

Index

Part I