Rashford, 18, made his first-team debut against Midtjylland in a Europa League match in February.
The former academy prospect’s rise has been meteoric, claiming a brace on his debut, another brace on his Premier League debut against Arsenal and scoring 138 seconds into his England debut.
Rashford’s strike for England meant he has netted nine goals in 19 appearances for club and country, and United have rewarded that fine form with a new long-term deal.
"I am delighted to have signed a new contract. I have always been a Manchester United fan, so to be playing in the first team really is a dream come true,” Rashford told the Manchester United official website.
" I am grateful for having the chance to prove myself. To be able to play football at the biggest club in the world means everything to me and my family."
Rashford’s new deal ties him to the club until 2020 with the option for another year.
"Marcus is a naturally talented footballer with great potential. He has taken his chances well and has integrated into the first team very quickly," said executive vice-chairman Ed Woodward.
" I am delighted that Marcus has signed a new contract, he is at the right club to continue his development."
Rashford’s team-mate Cameron Borthwick-Jackson also signed a new deal with the club.
Borthwick-Jackson made his Premier League debut against West Brom back in November and has signed a deal until 2020.
"I have grown up at United and have enjoyed every minute of being here," said Borthwick-Jackson. "Last season was an incredible experience to make my first team debut and a dream come true for myself and my family."
The 19-year-old made 10 Premier League appearances for United this season and was also voted their U21 player of the year.
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