Manchester United side acquired the Serbian midfielder from Chelsea for £40 million.
The midfielder turns to 29 today has signed a three year deal with the Red Devils side today and has an option to extend his deal further,
In EPL Matic has made 121 appearances for the Blues scored four goals for them.
Last season under the Italian manager Conte Matic has made 30 appearances for With Fabregas second place after Matic as both of the Midfielders vied for a spot along side Kante.
This season Chelsea also qualifies for the Champions league and the arrival of another French midfielder Tiemoue Bakayoko puts Matic’s position in a doubt.
Mourinho avouched in Manchester United official website: "Nemanja is a Manchester United player and a Jose Mourinho player. He represents everything we want in a footballer; loyalty, consistency, ambition, team player.
"I would like to thank him for his desire to join us because without that, it would be impossible to have him here. I am sure our players and supporters will love him. A big welcome to our new number 31."
Matic added: "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."