Timothy Fosu-Mensah, 18, whose previous terms had been due to expire at the end of the season, has signed a deal that has an option for a further year.
“I am delighted to have signed a new contract here at Manchester United,” Fosu-Mensah told the club’s official website.
“I have enjoyed every minute since I joined this great club and I want to continue the progress that I feel I have made so far.
“I am learning every day from the manager and the coaching staff. I appreciate the trust that the club has in me and I want to repay that with my performances on the pitch.”