WASHINGTON - President Barack Obama has chosen longtime trusted adviser and national security expert Denis McDonough as his fifth chief of staff.

A White House official said Obama will announce McDonough's appointment Friday. McDonough, 43, will take over the key role from Jack Lew, Obama's nominee for Treasury secretary.

McDonough has advised Obama on foreign policy for nearly a decade and most recently served as the president's deputy national security adviser. He is highly regarded by White House staffers.

McDonough's place in Obama's inner circle was illustrated during the Navy commando raid that killed Osama bin Laden in May 2011. He is among those whose images are captured in a White House photograph seated in the situation room with Obama and other senior officials watching the raid unfold.

The White House official, speaking on condition of anonymity in order to speak before the president's announcement, said McDonough has played a key role in all of Obama's major national security decisions in recent years, including the end of the war in Iraq, winding down the war in Afghanistan, responses to natural disasters in Haiti and Japan and repeal of the military's ban on openly gay service members.

Earlier, McDonough worked as a foreign policy specialist in Congress, including as a senior foreign policy adviser to former Senate Majority Leader Tom Daschle, a Democrat,  before moving to Obama's Senate office.