Kent-born McCallum began his career with Coventry City, then in League One, before signing for Norwich for a reported £3.7m in January 2020.
He was loaned straight back to the Sky Blues for what proved to be the Covid-terminated season, in which Coventry won promotion.
He made 60 appearances in his four and a half seasons at Carrow Road under three different managers – Daniel Farke, Dean Smith and David Wagner.
But that also included loan spells back at Coventry and also with Queens Park Rangers in 2021-22.
“The football United play is the football I want to be playing for the next couple of years,” said , externalMcCallum.
“I’ve always liked the football which the manager has implemented and hopefully I’ll fit hand-in-hand with that.”
