Brauchli's hiring was one of the first big moves by Weymouth, 46, who became publisher in February 2008.
Brauchli led the Post to four Pulitzer prizes. As the Post experienced declines in circulation and print advertising revenue, he also presided over a period of cost cutting, which included employee buyouts. The Post Co. sold its money-losing Newsweek magazine in 2010 for $1.
"Marcus has contributed immeasurably in the more than four years he has been at the helm of this newsroom," Weymouth said in a statement. "Under his leadership, we have become one newsroom publishing on multiple platforms, traffic has grown substantially and we are consistently recognized as among the most innovative mainstream news sites."
Brauchli's final day as executive editor will be Dec. 31.