NEW YORK—Marsh & McLennan Cos. Inc. said Monday that its board of directors has appointed Ian Lang as independent chairman of the insurance brokerage effective in May 2011.

Mr. Lang will succeed Stephen R. Hardis, who will step down next year in accordance with MMC’s mandatory retirement provision in its corporate governance guidelines, the New York-based insurance brokerage said in a statement.

Mr. Harris has held the Cleveland-based post since May 2006.

Joining MMC’s board in 1997, Mr. Lang has served as chair of its audit committee and since 2007 has been chair of its compensation committee.

He is based in London.