The former Germany captain, 32, has signed a one-year contract, according to the Chicago Tribune newspaper
“I’ve always sought opportunities where I hoped to make a positive impact,” Schweinsteiger said in the Tribune. “My move to Chicago Fire is no different.”
Schweinsteiger, who led Germany to World Cup victory in 2014, had talks with Chicago Fire last year but opted to stay at United beyond the end of the January window.
However, Fire requested the midfielder join them now and, as Schweinsteiger was unlikely to play any significant part at United for the remainder of the season, the Old Trafford club have sanctioned his exit.
Last week, he trained with some junior members of the United squad while the remainder prepared for their Europa League game against FC Rostov.
“In the locker room, he will be a huge example of a champion,” Chicago Fire manager Veljko Paunovic told the Tribune.
“He still is somebody that can show that on the field and [demonstrate] how our guys have to work, prepare, behave, think and work together in order to get to that level.”
Schweinsteiger, who was signed by the Old Trafford club under former boss Louis van Gaal in July 2015, trained alone or with the Under-23 side at United after Jose Mourinho took over as manager last summer.
He returned to the first-team set-up before a Europa League game against Fenerbahce in November and played his first game for the club this season in an EFL Cup win over West Ham on 30 November.
However, he has made just three further appearances for the club – scoring one goal – with his last outing coming as a substitute against Saint-Etienne in the Europa League on 22 February.