Greenwood is a graduate of Manchester United’s famed academy and has been with the Red Devils since the age of seven.
The striker became the youngest player in Manchester United’s history to start a Premier League game when Solskjaer handed him his full debut against Cardiff last season.
Although he is yet to start a Premier League game this season, the 18-year-old has made nine appearances under Ole Gunnar Solskjaer so far this season scoring two goals.
"Having grown up as a Manchester United fan, playing for the first team is a real dream come true," said Greenwood after his contract extension
"I know that, when I play for this club, I represent the whole academy and I want to repay the faith that my coaches have shown in me with my performances on the pitch.
"I am learning all the time from the manager and his coaching staff and I know that this is the perfect club to help me reach my potential."
Solskjaer paid homage to the teenager after an impressive start to his Manchester United senior career.
“Mason has progressed through our outstanding academy and we are delighted with the progress he has made,” Solskjaer said.
“At such a young age, he already has great pace and intelligence and he is such a natural finisher. Since he came into the first team, he has really impressed everyone with his drive and attitude, he has all the attributes to become a top player.
“Mason is learning every day in training and, with his work ethic, there is no doubt that he has an excellent future ahead of him.”
