The victory means that United, who finished eighth in the Premier League this season and 31 points behind champions City, secure a spot in the Europa League.
Manchester United have won the FA Cup after beating rivals Manchester City 2-1 in the final at Wembley.
Alejandro Garnacho put the Red Devils ahead with a close-range effort in the 30th minute after a mix-up between City defender Josko Gvardiol and goalkeeper Stefan Ortega.
Kobbie Mainoo then doubled United’s lead nine minutes later with a clinical finish.
United had a goal disallowed just before that when Marcus Rashford slotted home but Garnacho was judged to be offside.
Jeremy Doku pulled a goal back for City late in the second half but United clung on to secure victory and avenge their defeat to Pep Guardiola’s side in last season’s FA Cup final.
United co-owners Sir Jim Ratcliffe and Joel Glazer were in the stands at Wembley on Saturday, and the win means that the team, which finished eighth in the Premier League this season and 31 points behind champions City, have secured a place in the Europa League.
The triumph comes amid speculation that United manager Erik ten Hag is set to be sacked after a disappointing domestic league campaign.
A report on Friday claimed the Dutchman would be fired regardless of the outcome at Wembley.
If United had lost the final, they would not have been in Europe at all next season.
Following the victory, some United players dropped to their knees in celebration on the pitch, while others sprinted towards them from the technical area.
And a beaming Ten Hag got a congratulatory hug from City manager Guardiola after claiming his second piece of silverware in as many seasons, following last year’s League Cup victory.
Later, when asked if he had any idea about his future, Ten Hag told the BBC: “I don’t know. All I can do is prepare my team, develop my team, progress my team. This is a project. When I came in it was a mess, now we are better. But we are by far where we want to be.
“Football is about winning trophies. I want to play the best football. I want to play dynamic football. But you have to win games and trophies. That’s the mentality we’ve brought in. We only had one opportunity, the FA Cup and we did it. I’m so proud of the players and staff.”
Reporting from Wembley, Sky Sports’ Oliver Yew said: “Stunning scenes for Man Utd.
“The players are jubilant. The red flags are flying.”
He added: “They put a disappointing league season behind them to end the campaign with silverware.
“It was a tactical masterclass from Erik ten Hag, who wins a second trophy at Old Trafford, but will it be enough to keep him in a job? Only time will tell, but he will feel vindicated tonight after a brilliant afternoon from him and his side.”