United will be adding Dalot to their squad for the upcoming season, where he will face off against Antonio Valencia for the starting right back spot.
Dalot is seen as one of the most promising full back talents in Europe. United were able to acquire him for a modest fee of £17.4 million thanks to a release clause in his contract.
He has signed a five-year deal, which can be extended by a further year.
And his manager is delighted with the signing. In a statement on the club's website, Mourinho said: "Diogo is an extremely talented young defender with all the qualities to quickly become a great player for this club.
“He has all the attributes that a full-back needs: physicality, tactical intelligence and technical quality, combined with a Porto academy mentality which prepares players for the maturity they need at the professional level.
"In his age group, he is the best full-back in Europe and we all believe he has a bright future ahead of him at Manchester United."
United also announced the signing on Twitter:
Current mood #BemvindoDalot#MUFCpic.twitter.com/BFuaPgOH6R
— Manchester United (@ManUtd) June 6, 2018