White House Chief of Staff William M. Daley surprised President Barack Obama by resigning after a year at the start of the 2012 campaign.

Mr. Obama said Monday that Mr. Daley will be succeeded by White House budget director, Jack Lew, 56 years old.

The exit of Mr. Daley, a former J.P. Morgan Chase & Co. executive who was tasked with repairing the president’s soured relations with business and cutting deals with emboldened Republicans, reflects an election-year shift in White House strategy in which Mr. Obama is campaigning on a populist platform to energize the Democratic base.