Good help is hard to find. Apparently, it's also quite expensive.
The fee was not disclosed, but reports earlier in the week suggest the clubs settled on £80 million after clauses.
"I am delighted to have signed for this great club. I have thoroughly enjoyed my time at Leicester and would like to thank everyone at the club, and the fans, for their fantastic support over the past two seasons," Maguire said. "However, when Manchester United come knocking on your door, it is an incredible opportunity.
The imposing defender signed a six-year contract with the Red Devils. The deal includes an option for a seventh season.
Maguire, 26, is United's second big-money defensive recruitment of the summer after Aaron Wan-Bissaka made the Old Trafford pilgrimage from Crystal Palace for a reported £50-million fee.
It's safe to assume that Maguire, who joined Leicester two summers ago from Hull City for an initial £12 million, will pair with Victor Lindelof in Ole Gunnar Solskjaer's starting XI.
"Harry is one of the best center-backs in the game today and I am delighted we have secured his signature," Solskjaer said.
"He is a great reader of the game and has a strong presence on the pitch, with the ability to remain calm under pressure - coupled with his composure on the ball and a huge presence in both boxes - I can see he will fit well into this group both on and off the pitch."
Maguire represents an alternative to Matthijs de Ligt. The highly rated 19-year-old Dutchman was linked with a move to Manchester before swapping Ajax for Juventus on a £67-million transfer - roughly £13 million less than Ed Woodward and Co. paid for Maguire.