The highly-rated England youth international has moved to St. Andrew's on a youth loan until the end of the season, with the Red Devils having a 28-day recall option on him.
Blackett's main role is at left-back, but he can also play at centre-back or left-wing.
The Manchester-born player has been with United since he was just eight-years-old and was a member of their 2011 FA Youth Cup-winning squad.
Physically he is a powerful, strong and quick, and can strike a decent free-kick.
Earlier this season he spent a period out on loan at Sky Bet Championship side Blackpool, where he made five appearances for the Tangerines.