Having made over 50 appearances for the Red Devils, Diallo has been one of the standout performers under Amorim's tenure. The 22-year-old has netted six goals this campaign, including a crucial penalty against Manchester City and a late equalizer in the 2-2 draw with arch-rivals Liverpool.
"I'm absolutely delighted to sign this new deal", Diallo said. "I've had some incredible moments at this club but there is so much more to come. I have big ambitions for the game and I want to make history at Manchester United.''
"I've learned so much since joining Manchester United four years ago. I'm so grateful to the coaches and staff who have helped me develop, and to the fans who have pushed me on every day.''
"It's been a tough season for everyone, but I firmly believe we're on the right track and the future is going to be very special. I'm ready to give absolutely everything to help this team and make the fans proud again."
Manchester United's Technical Director, Jason Wilcox, added, "Everyone is thrilled with Amad's progress; his quality on the ball, versatility, and determination make him a vital part of Manchester United's future.
"The best years of Amad's career are ahead of him, and we're all looking forward to helping Amad fulfill his enormous potential and achieve success at the club in the coming seasons."
Diallo began this season on the fringes of the first team under former United boss Erik ten Hag, but grew frustrated with a lack of game time before Ten Hag was sacked in October and replaced by Amorim.
The Ivorian has previously enjoyed successful loan spells at Rangers and Sunderland, netting 14 goals in 42 appearances for the Black Cats during the 2022-23 campaign.
