The German World Cup winner, largely out of favour at Old Trafford under Jose Mourinho, has penned a one-year deal subject to a medical and visa.
"I am sad to leave so many friends at Manchester United," Schweinsteiger told United's official website. "But I am grateful to the club for allowing me the chance to take up the challenge at Chicago Fire.
I have enjoyed working with the manager, the players and staff here and wish them all the best in the future. But I have to reserve special thanks to the United fans – whose support has been a very special part of my time in Manchester.
Schweinsteiger made just four appearances for United this season, scoring one goal, after forcing his way back from exile and into the first team squad.
The 32-year-old will apparently earn $4.5 million (£3.6m) through his designated player contract in 2017 after the American club confirmed the move on their website.
Read the full article on eurosport.co.uk: Bastian Schweinsteiger signs for Chicago Fire