White House Chief of Staff William M. Daley resigned at the start of the presidential election year, a surprise decision that underscored President Barack Obama's shift toward a populist platform he hopes will win him another term this November.

Mr. Daley's move marked the end of a rocky yearlong tenure in which the former J.P. Morgan Chase & Co. executive, whose original mission was to reach out to business and congressional Republicans, became increasingly sidelined. Mr. Obama announced Monday that Mr. Daley would be succeeded...