McCallum, 23, is the club’s second summer recruit after ex-Leeds United utility player Jamie Shackleton was brought in earlier. He has signed a four-year contract.
The player, who was born in Kent, will provide United a useful alternative down the left side.McCallum declared: “I like the style of football, and it’s a big club.”
“I’ve always enjoyed the kind of football that the manager has brought to the team, and hopefully I’ll mesh well with it. I want to spend the next few years playing the kind of football that United plays.
“I am excited about all of the goals the manager has set for this place. I wanted to be involved because I believe the initiative is moving in the correct path moving forward.”
McCallum began his football career with non-league team Herne Bay. He later attended Jamie Vardy’s V9 Academy before receiving his big break with Coventry City.
After establishing himself inside the Sky Blues organisation, McCallum was loaned back to the Midlands club in January 2020, despite earning a £3.5 million move to Norwich.
Before establishing himself at Carrow Road and making 34 appearances in the previous season, McCallum had a brief stint at QPR and another loan at Coventry.
“Sam fits the profile, and we are excited to welcome him into the group,” manager Chris Wilder went on.
“He will infuse vitality into a part of the field where physical fitness is crucial. We aim to win games and be highly competitive in a division that is known for its toughness, and Sam’s enjoyment of taking the pitch and his championship experience will be invaluable.”