As one of Chicago's Designated Players, it is rumoured he will become one of the top earners in the league on an annual salary of around $4.5m - Kaka was the biggest earner in 2016, earning just over $7m at Orlando City.
"Throughout my career, I've always sought opportunities where I hoped to make a positive impact and to help make something great. My move to Chicago Fire is no different," he said in a statement published by Fire's official website.
Moving to Chicago certainly represents a challenge to Schweinsteiger. The club, MLS Cup winners in 1998, has finished bottom of the overall standings in each of the last two seasons and is desperate for improvement.
Fire general manager Nelson Rodriguez said, "We're adding someone who has won at every level, including the very highest levels, and has done so in a way that is consistent with our values.
"We as a club will now be forced to hold ourselves to a higher standard, an accountability level. Previously, I think we could satisfy ourselves with what is known domestically. Now we need to rise to a standard that is set more internationally."
Having joined United from Bayern Munich in 2015, Schweinsteiger was banished from the first-team squad by Mourinho after quickly being deemed surplus to requirements. He maintained a high level of professionalism, though, and eventually returned to the first-team fold.
Chicago's interest is thought to have begun before Christmas, while Schweinsteiger allegedly turned down a move to Sporting CP in summer - he often claimed he was never willing to play for any club in Europe other than Bayern or United.
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