MANCHESTER: After 18 years at Chelsea, Mason Mount became Manchester United's first signing of the off-season on Wednesday in a move worth 55 million pounds (USD 69 million).
The England international has signed a five-year deal with the option of a further 12 months.
The move comes a week after United reached an agreement with Chelsea, following protracted negotiations since the end of the season.
"It's never easy leaving the club where you grew up, but Manchester United will provide an exciting new challenge for the next phase of my career," Mount said.
"Having competed against them, I know just how strong a squad it is that I'm joining, and I can't wait to be part of this group's drive to win major trophies," he added.
United will have to pay a further 5 million pounds (USD 6.3 million) based on Mount meeting certain targets relating to appearances and success.
Mount was one of United manager Erik Ten Hag's leading targets ahead of the Dutchman's second season in charge at Old Trafford. He also wants to sign a top-class striker to replace Cristiano Ronaldo, who left in November.
Ten Hag is looking to build a squad capable of challenging for the Premier League title next season, as well as competing in the Champions League.
"Everyone can see that the club has made big steps forward under Erik ten Hag," Mount said.
"Having met with the manager and discussed his plans, I couldn't be more excited for the seasons ahead, and am ready for the hard work expected here. I am hugely ambitious; I know how amazing it feels to win major trophies and what it takes to do it. I will be giving everything to experience that again at Manchester United," he added.
Mount was part of Chelsea's Champions League-winning team of 2021 and has emerged as one of the Premier League's leading midfielders after coming through the club's academy. He also won the European Super Cup and Club World Cup with his former club.
He made 195 appearances for Chelsea and scored 33 goals. In his time at the club, he also established himself as a regular for England.
United football director John Murtough said, "Mason is an extremely intelligent footballer and has so many fantastic technical qualities that will significantly add to our squad."
He said, "We have admired his talents for a long time, so we are delighted that he has chosen to take the next steps in his career here at Old Trafford. Mason himself is a world-class player but he also has the ability to improve the players around him through his game intelligence and tactical awareness."
Mount posted an emotional video message to Chelsea fans on Tuesday to confirm he was leaving the club he joined as a six-year-old.
"Given the speculation over the last six months this may not come as a surprise to you, but it doesn't make it any easier to tell that I've made the decision to leave Chelsea," he said on Instagram.
"I know some of you won't be happy with my decision but it is what's right for me at this moment in my career," Mount added.
Mount is the latest player to leave Chelsea as part of a summer clear-out by the London club.
N'Golo Kante, Kai Havertz, Mateo Kovacic, Kalidou Koulibaly and Edouard Mendy are other high-profile players to leave, while Hakim Ziyech, Romelu Lukaku and Pierre Emerick Aubameyang are expected to follow.
The departures come after Chelsea spent around $630 million last season, but failed to qualify for Europe as it suffered its worst-ever Premier League campaign.