The firm said the move combines “diverse colleague” experience and shared values to drive distinctive outcomes for clients.
The transaction is also expected to generate more than $10bn (£7.6bn) in shareholder value creation from the capitalised value of expected pre-tax synergies.
“This transaction accelerates that journey by providing our combined teams the opportunity to drive innovation more quickly and deliver more value.”
Aon CEO, Greg Case, added: “This combination will create a more innovative platform capable of delivering better outcomes for all stakeholders, including clients, colleagues, partners and investors.
“Our world-class expertise across risk, retirement and health will accelerate the creation of new solutions that more efficiently match capital with unmet client needs in high-growth areas like cyber, delegated investments, intellectual property, climate risk and health solutions.”