He's held the post with the hotel chain twice before.
The first time was from 1993 to 2002, when he left to campaign for governor of Massachusetts, and from 2009 to 2011, when he left to start his campaign for the presidency.
It's the first job announcement Romney has made since being defeated in the November election by President Barack Obama.
Romney has kept a low profile since the election.
He's spent the past month largely in seclusion at his family's California home.
Marriott International Inc. is based in Maryland.