The deal between the both sides was agreed late Monday and subject to medical and visa being secured, the Chicago Tribune newspaper reports.
The American club are offering him a one-year contract worth £70,000 a week – which will make him one of the ten highest-paid players in the MLS .
“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.
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“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.
“I was delighted to be part of the squad that won the FA Cup for them last season and will always remember their energy and their passion. Now is the right time for me to start a new chapter in Chicago and I am looking forward to it.”
The 32-year-old was linked with a move overseas earlier this season but opted to stay at Old Trafford and fight for his place.
He joined Manchester United for around £14.5m from Bayern Munich in the summer of 2015.