CHICAGO—Gregory C. Case has signed a contract to remain Aon Corp.'s president and chief executive officer through April 3, 2015.

The Chicago-based broker said Monday that it has renewed Mr. Case's employment agreement for an additional five years. His agreement was set to renew in 2010.

Mr. Case joined Aon in April 2005 from consulting firm McKinsey & Co. to succeed Patrick G. Ryan, the broker's founder and longtime leader.

“Greg continues to do a terrific job leading Aon,” Lester B. Knight, nonexecutive chairman and director of Aon, said in a statement. “Under Greg's leadership, the firm is well-positioned to enhance shareholder value.”