Aon plc

Voting Matters

Shareholders are being asked to vote on the following matters at the Annual Meeting:

We are providing the enclosed proxy materials to you in connection with the solicitation by the board of directors (the “Board”) of Aon plc (“Aon” or the “Company”) of proxies to be voted at the annual general meeting of shareholders to be held on June 27, 2025 (the “Annual Meeting”), or any adjournment or postponement thereof. The Annual Meeting will be held at 70 Sir John Rogerson’s Quay, Dublin 2, Ireland. This proxy statement is first being mailed or made available to shareholders on or about April 28, 2025.

2025 Aon Proxy Statement 1

Who We Are

Aon is in the Business of Better Decisions

Aon exists to shape decisions for the better — to protect and enrich the lives of people around the world. Through actionable analytic insight, globally integrated Risk Capital and Human Capital expertise, and locally relevant solutions, our colleagues provide clients in over 120 countries with the clarity and confidence to make better risk and people decisions that protect and grow their businesses.

Our 3x3 Plan – with a focus on three commitments over three years (2024-2026) – is enabling Aon to go further, faster to address client need:

Through our 3x3 Plan we will accelerate our Aon United strategy to deliver critical outcomes for clients, colleagues and shareholders.

What We Do

Our Solutions

We are a leading global professional services firm providing a broad range of Risk Capital and Human Capital solutions. Through our experience, global reach and comprehensive analytics, we help clients meet rapidly changing, increasingly complex and interconnected risk and people challenges.

Corporate Sustainability and Risk

Management of corporate sustainability risks – including those related to environmental, social and governance (“ESG”) matters – is an increasingly important priority for our clients. At Aon, helping clients manage risk – including those relating to corporate sustainability and ESG – is at the core of what we do. We offer a wide range of risk assessment, consulting, and advisory solutions, many of which are significant parts of our core business offerings, designed to address and manage corporate sustainability and ESG issues for clients, and to enable our clients to create more sustainable value.

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As a professional services firm, Aon’s approach to risk management, including oversight of corporate sustainability and ESG risks, is a priority. The Board, as a whole and through its committees, oversees the Company’s ESG risks and opportunities, as well as related strategies, goals and objectives, and performance. The Board regularly reviews and discusses our ESG risks and opportunities, including Aon’s decarbonization and sustainability efforts and people-related risks, such as colleague satisfaction and engagement survey results, workforce engagement, pay equity, colleague well-being, talent retention and succession planning. We are committed to improving inclusion and wellbeing at Aon at all levels of our organization and have published certain of our workforce demographic data in our Annual Report on Form 10-K for the fiscal year ended December 31, 2024. Our EEO-1 Employer Information Summary Reports are available on our website at www.aon.com. Our Board is committed to continued adherence to effective corporate governance best practices, including oversight of enterprise risk management.

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2024 Highlights

In 2024, we delivered strong performance across each of our key financial metrics, in line with our objectives and guidance. Additionally, we completed the acquisition of NFP, meaningfully expanding our presence in the fast-growing middle market segment. We also returned $1.6 billion of capital to shareholders through share repurchases and dividends, highlighting our strong free cash flow generation and disciplined capital allocation model.

In assessing our performance, we focus on our performance against fournon-GAAP metrics that we communicate to shareholders: organic revenue growth, adjusted operating margin, adjusted diluted earnings per share, and free cash flow. Management believes that these measures are important to make meaningful period-to-period comparisons and that this supplemental information is helpful to investors. Management also uses these measures to assess operating performance and performance for compensation. Thesenon-GAAP metrics should be viewed in addition to, not instead of, our consolidated financial statements and notes thereto. A reconciliation of thesenon-GAAP metrics to the most directly comparable GAAP metrics is set forth in Appendix A to this proxy statement.

“Our strong performance in 2024 reflects outstanding execution across all aspects of our strategy. With year one of our 3x3 Plan complete, we have momentum and are well-positioned to drive long-term value creation for our colleagues, clients and shareholders.”

Greg Case, President and CEO

In 2024, we continued to deliver across these four metrics:

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Our Board of Directors

In August 2024, we announced that Admiral James Stavridis joined our Board effective August 15, 2024. Admiral Stavridis serves on the Finance Committee of the Board. On April 10, 2025, we announced that Fulvio Conti will be retiring from our Board effective at the Annual Meeting. Upon Mr. Conti’s retirement, our Board will be composed of 12 directors, 11 of whom are independent, including the Board Chair. It is a priority of the Governance/Nominating Committee to identify candidates for the Board of Directors who bring to our Board a wide variety of experiences, skills, qualifications and perspectives that strengthen their ability to carry out their oversight responsibilities.

Our Governance/Nominating Committee also considers a number of demographic and other factors in seeking to develop a Board that, as a whole, has the appropriate background, skills and experiences in the context of the needs of the Board.

As part of our ongoing Board refreshment process, we welcomed two new independent directors in 2024, four new independent directors since 2022, and seven new independent directors since 2016.

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Directors

• Independent director

† Number of current other public company directorships or listed business development company trusteeships

†† Mr. Conti is retiring effective at the Annual Meeting.

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Corporate Governance Highlights

Aon’s commitment to good corporate governance is integral to our business. Highlights of our strong corporate governance practices include:

2024 Executive Compensation Highlights

The core principle of our executive compensation program continues to be pay for performance, as we continue towards our goal of being the leading global professional services firm focused on risk, health, and wealth.

Leadership Performance Program. In early 2025, we settled performance share units (“PSUs”) granted to our NEOs in 2022 under our seventeenth LPP cycle (“LPP 17”). The settlement of those units in Class A Ordinary Shares was contingent upon achieving adjusted diluted earnings per share of at least $38.20 (threshold performance) over the performance period from January 1, 2022 to December 31, 2024, and reflects achievement of adjusted diluted earnings per share of $42.12, which exceeded the target performance level adjusted diluted earnings per share of $39.72. In 2024, we granted PSUs under our nineteenth LPP cycle (“LPP 19”) to each of our NEOs, which are expected to be settled in 2027 contingent upon the Company’s adjusted diluted earnings per share growth performance over the January 1, 2024 to December 31, 2026 performance period.

Annual Incentive Compensation. Annual incentives paid to our NEOs reflected our application of the incentive pool funding framework adopted by the Organization and Compensation Committee (the “Compensation Committee”), as well as the committee’s evaluation of each NEO’s contributions to our business and financial results, delivery of key strategic initiatives, and personal leadership qualities. The incentive pool funding determination included both a pre-established formulaic financial component (80% weighted), based on comparison of current year adjusted operating income results against the prior year, and a non-formulaic People & Culture component (20% weighted), based on Company’s progress across four areas: wellbeing, inclusion, engagement, and retention. Target annual incentive opportunities for our NEOs for 2024, as a percentage of base salary, remain unchanged from 2023. Once determined, annual incentives to our NEOs (other than Mr. Case) were paid 65% in cash and 35% in the form of time-vested restricted share units, which provides value to our executives that is tied to the long-term performance of the Company. Mr. Case’s annual incentive was paid 65% in the form of cash and 35% in the form of performance share units under our twentieth LPP cycle, as a further tie to the long-term

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Compensation-Related Best Practices

performance of the Company. Annual incentives for 2024 were awarded to our NEOs in early 2025 following the Company’s achievement of adjusted operating income of $4,939 million. The annual incentive awards are described in more detail in the section captioned “Annual Incentive Awards Under Our Shareholder-Approved Plan” below.

Our compensation philosophy and related governance features are complemented by several policies and practices designed to align our executive compensation program with the long-term interests of our shareholders, including the following:

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