Mary Schapiro, chairman of the Securities and Exchange Commission, announced her departure Monday, bringing to an end a turbulent period for the agency.

A career regulator, Schapiro is credited by current and former SEC officials with steadying the agency after its failure to spot the Bernard Madoff fraud, among others. Her experience in top regulatory roles helped to repair the SEC's battered image, protect its powers during a big rewrite of financial regulation law and boost employee morale.