Bryan Mbeumo says he has joined "the club of his dreams" after completing his move from Brentford for an initial £65m.
The 25-year-old has signed a five-year contract, with the option of a further 12 months.
He is manager Ruben Amorim's third signing of the summer after the arrivals of forward Matheus Cunha and left-back Diego Leon.
Mbeumo's move, seven weeks after United's first bid for the Cameroon international, brings to an end one of the longest-running sagas of the summer.
United's third offer, worth an initial £65m with £6m in add-ons, was accepted last week.
"As soon as I knew there was a chance to join Manchester United, I had to take the opportunity to sign for the club of my dreams; the team whose shirt I wore growing up," said Mbeumo.
"My mentality is to always be better than I was yesterday. I know that I have the spirit and character to reach another level here, learning from Ruben Amorim and playing alongside world-class players.
"Everybody told me about the environment that is being created here and how exciting the plans are for the future. This is a massive club, with an incredible stadium and amazing fans, we are all really determined to challenge for the biggest trophies."
United submitted their first bid for Mbeumo - worth an overall £55m - at the start of June.
They failed with a second bid of £62.5m at the end of that month before reaching an agreement with their third offer.
Mbeumo scored 70 goals and registered 51 assists in 242 games for Brentford since joining in 2019 from Troyes.
He netted 20 goals and registered seven assists in the Premier League last season - both career highs.
"Bryan's goals and assists record in the Premier League is exceptional, his remarkable consistency has put him among the most productive players in England for the last three seasons," said United director of football Jason Wilcox.
"Bryan's belief in our project and determination to join the club confirmed he was the perfect fit for Manchester United and the culture we are developing."
Mbeumo's departure makes him the Bees' biggest ever sale, eclipsing the £40m paid by Al-Ahli for Ivan Toney in August 2024.
"On behalf of everyone at Brentford, I would like to wish Bryan all the best for the future and thank him for his fantastic efforts over six seasons with us," said Bees director of football Phil Giles.
"Bryan came to us as a teenager, and it has been an absolute pleasure for all of us here to watch him develop as a player and a person. Our fans have loved him, and he has been a part of some of our greatest days.
"There is always a right time for a player to move on and, for Bryan, that time is now. He has the opportunity to go to one of the biggest clubs in the world and we are very happy for him."
The winger, who will wear the number 19 shirt, is expected to be in United's travelling squad for their pre-season tour of the United States on Tuesday.
