The 26-year-old joined the team he supported as a child in a £80m transfer from Leicester City this summer.
Maguire spoke of his excitement at joining his boyhood side after completing the move.
"It's a really proud moment for myself to join such a big club," he said, per the Manchester Evening News.
"You always dream of walking out at Wembley and Old Trafford they're the two big stadiums when you're a kid.
"An amazing club, it's a club I always watched and looked up to when I was younger. Now I'm part of it. The atmosphere in the stadium itself is so unique and something so special."
Maguire has been one of the best centre-back's in the Premier League for the past few years.
And it wasn't just United that were keen to sign him.
Speaking after his side's win against Liverpool in the Community Shield, Guardiola revealed City were priced out of a deal for the defender.
"He's an excellent, top-class player," he said last week, per the BBC.
"We were interested but could not afford it. United could afford it."
However, according to the Daily Star, the Citizens actually made an eye-watering offer to the England international this summer.
They claim City offered £278,000-per-week to Maguire in a deal that would make him the highest paid defender in the world.
However the money was irrelevant to Maguire who turned it down and instead accepted a £190-per-week offer from Man United instead.
That means Maguire had the chance to earn around £90,000 more than he is now.
Maguire is already well thought of among United fans and this is bound to win him over even more support from his own fans.
Guardiola also congratulated United for managing to acquire Maguire.
"He had an incredible World Cup. He's strong in the air, good with the ball and builds it up, he's so fast. He's young. Congratulations to United."News Now - Sport News