Dalot's new five-year deal includes the option of a further season as the right-back is rewarded for an impressive season with the club.
Erik ten Hag's team finished third in the Premier League, won the League Cup and face Manchester City in the FA Cup final on Saturday.
Dalot, capped 11 times by Portugal, joined United from Porto in 2018 and has gone on to make 107 appearances in all competitions.
Dalot, who spent the 2020/21 season on loan at AC Milan, said: "Playing for Manchester United is one of the highest honours that you can have in football.
"We have shared some fantastic moments over the past five years and I've grown so much and my passion for this incredible club has only increased since the day that I joined.
"As a group of players, we all feel like we are at the start of a special journey right now.
"I can assure you that I will dedicate myself relentlessly to helping this group to achieve our aims and make the fans proud of this team.
"That drive continues this week with everyone intensely focused on preparations for the FA Cup final."
