Obama called Carney one of his closest advisers and friends at the White House in remarks to the press in the White House briefing room.
Deputy Josh Earnest will take over the job as the president's press secretary.
"Today the flak jacket is officially passed to a new generation," he said of Earnest.
Carney, 49, a former TIME Magazine White House correspondent, joined the administration in late 2008 as spokesman for Vice President-elect Biden. He was promoted to Obama's chief spokesman in Feb. 2011, replacing Robert Gibbs.