News of the transfer came from the club's official Twitter account on Friday:
On Thursday, the midfielder posted the following snap at the airport on the way to joining his new club:
According to James Robson of the Evening Standard, the Red Devils will get a fee of around £10.5 million for Fellaini.
The 31-year-old moved to Old Trafford from Everton in 2013 to join forces with former manager David Moyes, but he struggled to settle in with his new club. The Daily Telegraph ranked him among the worst transfer moves of the 2013-14 campaign, and things barely got better the following season.
Louis van Gaal, Moyes' successor, often made use of the physical Belgian as a battering ram in midfield, but he was always more suited in an attacking role that was hard to come by for him at Old Trafford.
Fellaini became less and less popular with the fans as time wore on, and when Jose Mourinho replaced Van Gaal as United boss, speculation he could be sold started to surface.
Mourinho made frequent use of Fellaini, however, and the Belgian greatly improved his form during the Special One's first season. He was eventually overtaken in the pecking order by Ander Herrera but continued to see minutes all over midfield. He impressed in the 2017 UEFA Europa League final that United won 2-0 over Ajax.
Fellaini was even better in the 2017-18 campaign, resulting in a surprise new contract. That deal only served to prolong Fellaini's spell at Old Trafford for another half a season, however, with Mourinho leaving the club in December. With his biggest supporter gone, Fellaini's days were numbered.
Alex Shaw of ESPN.com praised the application of Fellaini during his time at United:
He becomes the fourth Belgium international to move to the Chinese Super League, following in the footsteps of Axel Witsel, Yannick Carrasco and Mousa Dembele. The latter made the switch from Tottenham Hotspur earlier this transfer window, while Witsel has returned to Europe and flourished with Borussia Dortmund.