Siccardi, who has held a number of roles since joining Aon in 2006, will report to UK CEO Nick Frankland and CFO Maggie Westdale.
The new COO will oversee the strategy, development and execution of policy and practice in all operational areas of the UK business, and will be responsible for building a platform for the firm’s growth.
Siccardi will perform her new role concurrently with her current responsibilities as Aon Benfield’s Europe, the Middle East and Africa and UK head of client services.
Frankland said: “I look forward to Leonora Siccardi’s expanded contribution to the Aon Benfield executive committee in London and the UK leadership group.”
He added: “Her understanding of the interaction and synergy between the front and back ends of our operating model will be invaluable in improving both our internal efficiency and the overall client experience.”