Jason Holtman has left his role overseeing PC gaming and entertainment strategy at Microsoft after just six months.
"We can confirm that Jason has left Microsoft and we're grateful for his time at the company," Microsoft told Polygon.
"We wish him the best in his future endeavours."
Holtman was the director of business development for Valve for almost eight years, before leaving in February 2013.
In August 2013 he joined Microsoft, where he hoped to use his Steam experience to make the Windows OS a better experience for gamers.
"Yes, I have joined Microsoft where I will be focusing on making Windows a great platform for gaming and interactive entertainment," he said.
"I think there is a lot of opportunity for Microsoft to deliver the games and entertainment customers want and to work with developers to make that happen, so I'm excited to be here."
Holtman has yet to comment publicly on the move.