Stephen R. Hardis, chairman of MMC's board, hailed the new CEO's arrival by noting in a statement that, “Throughout his career, including 10 years as a CEO, Brian Duperreault has proven his ability to produce results and create shareholder value. We are delighted to welcome him to MMC.”

Mr. Duperreault said: “I am honored to become the CEO of MMC, a company that comprises several of the world's greatest brands in risk and insurance services and consulting. I look forward to working with the company's talented executives.”

He added that MMC is “an institution with unrivaled resources and capabilities. My mission is to capitalize on the strength of MMC's operating companies to deliver value to clients, employees and shareholders.”

From 1994 to 2004, Mr. Duperreault served as CEO of ACE Ltd., the Bermuda-based insurer MMC helped found in 1985. He served as ACE chairman from 2004 to 2007. ACE's net premiums are currently $12 billion.

Describing Mr. Duperreault's tenure at ACE, MMC said he had grown the firm “from a boutique catastrophe insurance specialist into a global multi-line commercial enterprise. He presided over significant organic growth as well as the acquisition of several businesses, including the 1999 acquisition of Cigna's property and casualty business.”

Under Mr. Duperreault, ACE's market capitalization grew from $1.1 billion to approximately $19 billion today.

Prior to ACE, Mr. Duperreault was with American International Group for more than 20 years, holding numerous positions, eventually becoming executive vice president of AIG Foreign General Insurance and chairman and CEO of AIG's American International Underwriters, which comprises all of AIG's non-U.S. commercial business.

In addition to Marsh, MMC is the parent company of Guy Carpenter reinsurance brokerage; Kroll, a risk consulting firm; Mercer, a provider of human resources and related financial advice and services; and Oliver Wyman, a management consultancy.

The firm has more than 55,000 employees, annual revenue of $11 billion and a presence in more than 100 countries.

Jeffrey Greenberg's brother, Evan S. Greenberg, ACE's chairman and CEO, issued a statement wishing Mr. Duperreault the best with his job at MMC, which he called “a great global franchise and an important presence in our industry.”

He added that “we have every confidence that Brian will provide the same exceptional leadership to Marsh & McLennan that he gave to ACE for so many years and for which we will always be grateful. We look forward to working with Brian and all of his new colleagues.”