The 23-year-old has signed a five-year contract with the option of a sixth season after United agreed a deal with Juventus.
The £89m figure eclipses the £85m that Real Madrid paid Tottenham for Gareth Bale in 2013.
Pogba left United four years ago for a nominal fee, and went on to win four Serie A titles and the Coppa Italia twice while his reputation grew - persuading Jose Mourinho to pay a colossal sum to bring him back to Old Trafford.
"I am delighted to rejoin United," Pogba said. "It has always been a club with a special place in my heart and I am really looking forward to working with Jose Mourinho.
"I have thoroughly enjoyed my time at Juventus and have some fantastic memories of a great club with players that I count as friends.
"But I feel the time is right to go back to Old Trafford. I always enjoyed playing in front of the fans and can't wait to make my contribution to the team.
"This is the right club for me to achieve everything I hope to in the game."
Additional reporting by PA.
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