Harry Maguire discusses his move to Manchester United from Leicester City
The 26-year-old was strongly linked with both Manchester clubs over the summer but Leicester held out for their valuation to be met.
The fee surpassed the £75million Liverpool paid Southampton for Virgil Van Dijk in January 2018.
Maguire could make his debut in Manchester United's Premier League season opener against Chelsea at Old Trafford on Sunday.
He becomes United manager Ole Gunnar Solskjaer's third summer signing, after right-back Aaron Wan-Bissaka arrived from Crystal Palace and winger Daniel James joined from Swansea.