Exhibit 99.1

NEWS RELEASE

ARTHUR J. GALLAGHER & CO. ANNOUNCES

FOURTH QUARTER AND FULL YEAR 2021 FINANCIAL RESULTS

ROLLING MEADOWS, IL, January 27, 2022 — Arthur J. Gallagher & Co. (NYSE: AJG) today reported its financial results for the quarter and full year ended December 31, 2021. Management will host a webcast conference call to discuss these results on Thursday, January 27, 2022 at 5:15 p.m. ET/4:15 p.m. CT. To listen to the call, and for printer-friendly formats of this release and the “Supplemental Quarterly Data” and “CFO Commentary,” which may also be referenced during the call, please visit ajg.com/IR. These documents contain both GAAP and non-GAAP measures. Investors and other users of this information should read carefully the section entitled “Information Regarding Non-GAAP Measures” beginning on page 10.

Summary of Financial Results - Fourth Quarter

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“We delivered an outstanding fourth quarter, wrapping up another excellent year of financial performance!” said J. Patrick Gallagher, Jr., Chairman, President and CEO. “During the quarter, our core brokerage and risk management segments combined to post 18% growth in revenue, of which 11% was organic revenue growth; net earnings growth of 11%; and adjusted EBITDAC growth of 17%. We completed 18 new tuck-in mergers and our newly acquired reinsurance operations had a strong December.

“Overall, the P/C renewal premium increases we saw during the quarter were consistent with the first three quarters of 2021. P/C rates continued to move higher across nearly all geographies and lines of coverage, insured exposure unit changes were positive, and inflation is at levels not seen for several decades. For the third straight quarter we benefited from positive policy endorsements and other mid-term policy adjustments, indicating a rebound in the underlying economic health of our clients, notwithstanding the late-year surge in COVID-19 cases.

“Within our benefits and HR consulting business we saw rising covered lives and strong demand for special project work. And in our risk management and claims paying unit, Gallagher Bassett, we had an excellent finish to the year fueled by new business wins and claim count increases.

“I am extremely pleased with how our businesses performed during 2021 and that our 39,000 colleagues continue to deliver the very best insurance and risk management advice to clients and prospects, day-in and day-out. We have terrific momentum, which makes me bullish about our prospects in 2022 and beyond!”

Summary of Financial Results - Year Ended December 31,

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Acquisition of the Willis Towers Watson Treaty Reinsurance Brokerage Operations

On December 1, 2021, we acquired substantially all of the Willis Towers Watson treaty reinsurance brokerage operations for an initial gross consideration of $3.25 billion, and potential additional consideration of $750 million subject to certain third-year revenue targets. There are twelve remaining international operations with deferred closings that comprise approximately $180 million of the initial purchase consideration that are subject to local regulatory approval and are expected to close in the first and second quarters of 2022. We funded the transaction using cash on hand, including $1.4 billion of net cash raised in our May 17, 2021 follow-on common stock offering, $850 million of net cash borrowed in our May 20, 2021 30-year senior note issuance, $750 million of net cash borrowed in our November 9, 2021 10-year ($400 million) and 30-year ($350 million) senior note issuances and short-term borrowings.

Impact of COVID-19 Pandemic Recovery

Relative to fourth quarter 2020, during fourth quarter 2021:

If economic conditions continue to improve, we believe we may continue to see favorable revenue benefits in our Brokerage and Risk Management segments in the first quarter of 2022 relative to the same quarter in 2021. However, if the economic recovery slows, due to the Omicron variant or other factors, we could see less revenue benefits than we experienced in the second, third and fourth quarters of 2021.

During the second, third and fourth quarters of 2020 and first quarter of 2021, we realized significant expense savings (totaling approximately $60 million to $75 million per quarter relative to the prior year same quarters, adjusted for pro forma full-quarter costs related to acquisitions) as a result of reduced travel, entertainment and advertising expenses, reduced costs from lower employee medical plan utilization, a reduction in workforce, wage controls, and reduced use of external consultants. During the second, third and fourth quarters of 2021, as we increased our business activities relative to the second, third and fourth quarters of 2020, we experienced increases in travel and entertainment, full restoration of advertising and more normalized usage of our employee medical plan, resumption of annual support-layer wage increases, increased use of external consultants, further investment in support of our hybrid employee environment, continued investment in cyber security and an increase in incentive compensation. These incremental costs totaled approximately $15 million, $25 million and $30 million in our Brokerage segment relative to the second, third and fourth quarters of 2020, respectively. Looking forward to 2022, we believe we will see incrementally higher Brokerage segment costs relative to 2021, and if the pace of economic recovery accelerates beyond our expectations, we could see expense increases higher than our current estimates.

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Brokerage Segment Reported GAAP to Adjusted Non-GAAP Reconciliations (dollars in millions):

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Brokerage Segment Reported GAAP to Adjusted Non-GAAP Reconciliations (continued) (dollars in millions):

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Brokerage Segment Reported GAAP to Adjusted Non-GAAP Reconciliations (continued) (dollars in millions):

Risk Management Segment Reported GAAP to Adjusted Non-GAAP Reconciliations (dollars in millions):

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Risk Management Segment Reported GAAP to Adjusted Non-GAAP Reconciliations (continued) (dollars in millions):

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Corporate Segment Reported GAAP Information (dollars in millions):

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Interest and banking costs and debt - At December 31, 2021, Gallagher had $1,600.0 million of borrowings from public debt, $4,448.0 million of borrowings from private placements and $45.0 million of short-term borrowings under its line of credit facility. In addition, Gallagher had $228.4 million outstanding under a revolving loan facility that provides funding for premium finance receivables, which are fully collateralized by the underlying premiums held by insurance carriers, and as such are excluded from our debt covenant computations.

Clean energy - Consists of the operating results related to our investments in clean coal production plants and royalty income from clean coal licenses related to Chem-Mod LLC. Additional information regarding these results is available in the “CFO Commentary” at ajg.com/IR.

Acquisition costs - Consists mostly of external professional fees and other due diligence costs related to acquisitions. On occasion, Gallagher enters into forward currency hedges for the purchase price of committed, but not yet funded, acquisitions with funding requirements in currencies other than the U.S. dollar. The gains or losses, if any, associated with these hedge transactions is also included.

Corporate - Consists of overhead allocations mostly related to corporate staff compensation, other corporate level activities, and net unrealized foreign exchange remeasurement. In addition, includes the tax expense related to partial taxation of foreign earnings, nondeductible executive compensation and entertainment expenses and the tax benefit from vesting of employee equity awards.

Income Taxes

Gallagher allocates the provision for income taxes to its Brokerage and Risk Management segments using the local country statutory rates. Gallagher’s consolidated effective tax rate for the quarters ended December 31, 2021 and 2020 was (7.0)% and (14.5)%, respectively, which was lower than the statutory rate due to the production of IRC Section 45 clean energy tax credits. In third quarter 2020, Gallagher increased its estimated U.K. effective income tax rate from 17.5% to 19%. In second quarter 2021, the U.K. government enacted tax legislation that increases the corporate income tax rate from 19% to 25% effective in 2023. Gallagher incurred additional income tax expense during 2021 to adjust certain deferred income tax liabilities to the higher income tax rate.

Webcast Conference Call

Gallagher will host a webcast conference call on Thursday, January 27, 2022 at 5:15 p.m. ET/4:15 p.m. CT. To listen to this call, please go to ajg.com/IR. The call will be available for replay at such website for at least 90 days.

About Arthur J. Gallagher & Co.

Arthur J. Gallagher & Co., an international insurance brokerage and risk management services firm, is headquartered in Rolling Meadows, Illinois, has operations in 68 countries and offers client-service capabilities in more than 150 countries around the world through a network of correspondent brokers and consultants.

Cautionary Information

This press release contains “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. When used in this press release, the words “anticipates,” “believes,” “contemplates,” “see,” “should,” “could,” “will,” “estimates,” “expects,” “intends,” “plans” and variations thereof and similar expressions, are intended to identify forward-looking statements. Examples of forward-looking statements include, but are not limited to, statements regarding changes in our expenses in the next several quarters; the impact of the COVID-19 pandemic recovery; anticipated future results or performance of any segment or the Company as a whole; the premium rate environment and the state of insurance markets; and the economic environment.

Gallagher’s actual results may differ materially from those contemplated by the forward-looking statements. Readers are therefore cautioned against relying on any of the forward-looking statements, which are neither statements of historical fact nor guarantees or assurances of future performance. Important factors that could cause actual results to differ materially from those in the forward-looking statements include changes in worldwide and national economic conditions, including the pace of economic recovery following COVID-19; our actual acquisition opportunities; or other factors like a military conflict between Russia and Ukraine; trade wars or tariffs; political unrest in the U.S. or other countries around the world; changes in premium rates and in insurance markets generally; and changes in the insurance brokerage industry’s competitive landscape.

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In particular, the global spread of COVID-19 has created significant volatility and uncertainty and economic disruption that may impact our forward-looking statements. The extent to which the pandemic impacts our business, operations and financial results will depend on numerous evolving factors, many of which are not within our control and that we may not be able to accurately predict, including: its duration and scope; the effectiveness of vaccines, how quickly vaccines are distributed and administered, and our employees’ and the general population’s willingness to receive them; governmental, business and individuals’ actions that have been and continue to be taken in response to the pandemic, including vaccine mandates, which could be controversial for some employees; the impact of the pandemic on economic activity and actions taken in response; the effect on our clients and client demand for our services; our ability to sell and provide our services, including limitations on travel and difficulties of our clients and employees working from home and closure of their facilities; the ability of our clients to pay their insurance premiums which could impact our commission and fee revenues for our services; the nature and extent of possible claims that might impact the ability of underwriting enterprises to pay supplemental and contingent commissions; the number of new arising workers’ compensation and general liability claims; and the long-term impact of employees working from home, including increased technology costs, and employees’ holistic wellbeing.

Please refer to Gallagher’s filings with the SEC, including Item 1A, “Risk Factors,” of its Annual Report on Form 10-K for the fiscal year ended December 31, 2020, its subsequently filed Quarterly Reports on Form 10-Q and the prospectus filed on November 3, 2021 for a more detailed discussion of these and other factors that could impact its forward-looking statements. The COVID-19 pandemic currently amplifies, and in the future could continue to amplify, the risks, uncertainties and assumptions, reflected in such risk factors. Any forward-looking statement made by Gallagher in this press release speaks only as of the date on which it is made. Except as required by applicable law, Gallagher does not undertake to update the information included herein or the corresponding earnings release posted on Gallagher’s website.

Information Regarding Non-GAAP Measures

In addition to reporting financial results in accordance with GAAP, this press release provides information regarding EBITDAC, EBITDAC margin, adjusted EBITDAC, adjusted EBITDAC margin, diluted net earnings per share, as adjusted (adjusted EPS), adjusted revenue, adjusted compensation and operating expenses, adjusted compensation expense ratio, adjusted operating expense ratio and organic revenue. These measures are not in accordance with, or an alternative to, the GAAP information provided in this press release. Gallagher’s management believes that these presentations provide useful information to management, analysts and investors regarding financial and business trends relating to Gallagher’s results of operations and financial condition or because they provide investors with measures that our chief operating decision maker uses when reviewing the company’s performance. See further below for definitions and additional reasons each of these measures is useful to investors. Gallagher’s industry peers may provide similar supplemental non-GAAP information with respect to one or more of these measures, although they may not use the same or comparable terminology and may not make identical adjustments. The non-GAAP information provided by Gallagher should be used in addition to, but not as a substitute for, the GAAP information provided. As disclosed in its most recent Proxy Statement, Gallagher makes determinations regarding certain elements of executive officer incentive compensation, performance share awards and annual cash incentive awards, partly on the basis of measures related to adjusted EBITDAC.

Adjusted Non-GAAP presentation - Gallagher believes that the adjusted non-GAAP presentations of the current and prior period information presented in this earnings release provide stockholders and other interested persons with useful information regarding certain financial metrics of Gallagher that may assist such persons in analyzing Gallagher’s operating results as they develop a future earnings outlook for Gallagher. The after-tax amounts related to the adjustments were computed using the normalized effective tax rate for each respective period. See pages 14 and 15 for a reconciliation of the adjustments made to income taxes.