He will be succeeding Hooman Kaveh, who will assume the newly-created role of executive chair for Mercer’s investment platform. O’Sullivan and Kaveh will report to Michael Dempsey, Mercer’s president for investments and retirement, and will remain based in Dublin.

As global chief investment officer, O’Sullivan will lead the range of Mercer’s investment capabilities, from research to investment solutions and performance, across traditional and alternative asset classes. He will also enable Mercer’s investment colleagues to operate across the continuum of tools, advice and implementation, playing a role in integrating the investment expertise and capabilities gained from recent acquisitions. In future, all asset class teams will report to O’Sullivan, the firm said in a statement.

“Niall’s deep knowledge of our investment business, passion for achieving strong investment outcomes for our clients, and ability to foster high-performing teams will position us strongly for the future,” said Dempsey. “Continuing to work together, both Niall and Hooman will help accelerate the integration of our expanding investment capabilities, scale our differentiated offerings, and deliver consistent, impactful outcomes for our clients.”

In his new capacity, Kaveh will lead initiatives such as a focusing on M&A, integrating AI into Mercer’s investment processes, and providing custom training and development resources to help colleagues optimise Mercer’s expanding range of investment capabilities. He will continue to chair the firm's investment governance committee, the firm added.