Concise News reports that Maguire, 26 passed his medical on Monday and was unveiled as a player of the Europa League campaigners.
After the official confirmation of his transfer, the England international spoke with MUTV in his first interview as a Red soldier.
Thanks to everyone who has supported me and played a part in my career.
— Harry Maguire (@HarryMaguire93) August 5, 2019
“It’s incredible,” Maguire said.
“A really proud moment for myself, to join such a big club, one that I’m really looking forward to it and I can’t wait to get started now.
“My first game of last season was at Old Trafford and it’s a fixture I always look for when I’ve been playing in the Premier League. Old Trafford away, and it’s now my home.
“I tend to get my head down – I’ve worked hard and done every session and I’ve played every game for Leicester, so I feel my fitness is there.
“That was a big part for me to play because, if I ended up getting the move that I wanted, I would have been fit and in contention to play the first game.
“I feel like I’m ready to go, but obviously it’s the gaffer’s decision.”
Maguire is determined to win silverware with his new club and also has a message for the supporters.
“It’s a young team now and I think we’ve got big ambitions for the future,” he added.
“We’ve got to start winning trophies again and it’s something the gaffer wants to bring to the club – the winning mentality as well, which will help all the boys. I’m sure it’s something he and his staff will bring to the club and we’re all looking forward to it.
“I’m really proud to be here, at such a big club, and I’m really looking forward to getting started. I’m hoping it will be a successful season, and I’ll give everything I’ve got for this club.”
United begin the new Premier League season against Chelsea at Old Trafford on Sunday.