The midfielder leaves Chelsea having made 151 appearances during his second spell at Stamford Bridge, but the defensive midfielder has revealed that he did not want to turn down a reunion with former boss Jose Mourinho.
The 28-year-old told the club’s official website: “I am delighted to have joined Manchester United. To work with Jose Mourinho once again was an opportunity I couldn’t turn down.
“I have enjoyed my time at Chelsea and would like to thank the club and the fans for their support. I cannot wait to meet my new team-mates and to start training with them.
“This is a very exciting time for the club and I am looking forward to playing my part in creating more history for this great club.”