The 25-year-old Cameroon international has put pen to paper on a five-year deal with Manchester United, keeping him at the club until 2030 with the option of a further 12 months.
Mbeumo joins Manchester United from Brentford for a reported fee of £65 million plus £6 million in add-ons, ending one of the summer's longest transfer sagas.
Arsenal, Tottenham, and Newcastle had all been linked with a move for Mbeumo, but he has chosen to join Manchester United instead.
In a statement to the club's in-house media team, Mbeumo said: "I had to take the opportunity to sign for the club of my dreams. 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."