The United academy product made his debut against Swansea on the opening day of the season and has since gone on to make another nine appearances for the club.
The 20-year-old’s contract was due to expire in the summer, but he has agreed a new deal that will keep him at the club until June 2017, and there is an option to extend by another year.
“I am delighted that Tyler has signed a new contract,” said United manager Louis van Gaal, who handed another academy product, Paddy McNair, a new contract earlier this month.
“He is another young player that has risen through the academy system to break into the first-team squad this season.
“Tyler has great potential and I believe he is at the right club to continue his development and progression to become a great defender.”
Van Gaal is keen to promote youth players from the academy and although Blackett has not played since January 11, he is clearly in the Dutchman’s long-term plans.
Blackett, who hails from Hulme, which is within two miles of Old Trafford, was delighted to commit his future to a club he has been at for the last 12 years.
“I’m thrilled to have signed my new contract,” the defender said.
“I have supported United all my life and have been here since I was eight years old.
“To come through the academy and make my debut this season was a dream come true.
“I want to keep improving within the first-team squad with the help of the manager, coaches and the players around me.”