Greenwood, who has been at United since the age of seven, has put pen to paper on a new deal which will keep him at the Premier League and European giants until June 2025, with the option to extend for a further year.
The England international has broken into the first team and is now a key member of manager Ole Gunnar Solskjaer’s squad.
The 19-year-old forward has made 12 starts and six substitute appearances in the Premier League for United so far this season, scoring one goal and providing one assist in the process.
The teenager has also made two starts and three substitute appearances in the Champions League for the Red Devils so far this campaign, scoring one goal and providing one assist in the process.
Greenwood told United’s official website: “When you join the club at seven years old, you just dream of playing for the first-team one day. I’ve worked so hard to reach this level and the last two years have been amazing. There is so much that I want to achieve in the game and I know that this is the perfect environment to play my football.
“With the support from the manager, his coaching staff and so many great players to learn from; I know that I am developing every single day. There is a lot more to come from myself and this team and I am so committed to working hard week in, week out to help the group achieve success.
“I want to repay the club for the support that everyone has given me over the years and show everyone just what I am capable of.”
Solskjaer said: “Mason is a fantastic talent and yet another fine example of the type of player that our Academy produces. He has made great progress this season, showing real maturity and adaptability to his game, which has seen him develop into one of the best young players in the country.
“Whilst it is easy for people outside of the club to forget that Mason is just 19, it is our job as coaches to ensure he reaches his phenomenal potential and every step we take is to help him along that path.
“Mason is naturally gifted and has a brilliant attitude; we know how important he is going to be for Manchester United over the coming seasons.”