Weymouth's departure is the end of an era of Graham family involvement with the Post. Her great-grandfather bought the newspaper in the 1930s, and her uncle Donald Graham sold it to Bezos last August for $250 million.
She'll be replaced by Frederick J. Ryan, the founding CEO of Politico and a former Reagan administration official.
Bezos declined to comment to the Post on the reasons behind the switch, but the Amazon founder had been looking to expand the Post's editorial staff with a focus on its digital side.
Ryan told the Post in an interview that he planned to keep executive editor Marty Baron and editorial page editor Fred Hiatt on board.