The decision makes Ms. White, a former federal prosecutor who has served more than two decades in the federal government, the first major Obama administration appointee to step down after Donald J. Trump’s upset victory last week. Other financial regulators are expected to follow suit in the coming weeks.
The election of Mr. Trump is a game-changer for the S.E.C. — and for that matter, all financial agencies.
Ms. White was expected to leave no matter the outcome of the election. But many Democrats had hoped that if Hillary Clinton won, she would choose a strong proponent of regulation to succeed Ms. White, whose policies often reflected a political middle ground. Now, the agency is almost certain to be pushed to the right.