The Red Devils paid £18million to land the player, who has put pen to paper on a five-year deal at Old Trafford, with the option of a further season.
He made a total of 38 appearances for Swansea across all competitions in the 2018/2019 season, notching five goals and making 10 assists. The Premier League is the best league in the world and Manchester United is the flawless place for me to continue to develop as a player.
"I am looking forward to working with Ole, meeting the team and getting started, " James said."This is the flawless environment for Daniel to continue his development".
Speaking to the official United website, James said: "This is one of the best days of my life and a challenge I am really looking forward to".
Meanwhile, he will have a little less pressure and time to adjust as Manchester United were unable to finish among the top four and will not play in next term's intense Champions League.
"I think the ambition they've got for the club is incredible for the next few years - to get players in who are hungry and ready to work hard".
The 21-year-old described himself as a "versatile and pacey player" that can play in different positions.
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The Welshman claims Manchester United is "the flawless place" for him to develop.
His potential has clearly caught the attention of Man Utd as he's now become Ole Gunnar Solskjaer's first major signing of the summer window and he should prove to be an exciting addition to their squad.
Meanwhile, legendary boss Ferguson splashed a healthy £250,000 to lure Viv Anderson from Arsenal in 1987.
A centre back is high on his priority list, with Napoli's Kalidou Koulibaly, Bayern Munich's Jerome Boateng and in demand Ajax wonder kid Matthjis de Ligt all linked with a move to United.
Solskajer's first signing follows in the footsteps of his predecessors Jose Mourinho, Louis van Gaal, David Moyes and Sir Alex Ferguson.