The 39-year-old Portuguese coach, who won two Primeira Liga titles with Sporting Lisbon, has signed a deal until 2027 and will join the club on November 11.
“Manchester United is delighted to announce the appointment of Ruben Amorim as head coach of the men’s first team, subject to work visa requirements,” the club said on its website.
“He will join until June 2027 with a club option of an additional year, once he has fulfilled his obligations to his current club.”
United described Amorim as “one of the most exciting and highly rated young coaches in European football”.
United sacked Ten Hag on Monday after a 2-1 defeat by West Ham left them languishing 14th in the Premier League, with just three wins from nine matches.
Ruud van Nistelrooy took charge following Erik Ten Haag’s departure on Tuesday. He will still be in the dugouts for the upcoming 3 matches.
They will face a big domestic game against Chelsea on Sunday, while playing Leicester City on 10 November.
Sandwiched between this he will face the task of getting their Europa League campaign back on track against PAOK from Greece next Thursday.
Amorim quickly emerged as the club’s top target and Sporting issued a statement to the Lisbon stock exchange earlier this week confirming United were willing to meet his release clause of 10 million euros ($11 million).
Amorim was peppered with questions about his prospective switch at his press conference ahead of Sporting’s home league game against Estrela on Friday but he remained tight-lipped.
“It is a negotiation between two clubs,” he said on Thursday.
“It’s never easy. Even with the clauses it’s never easy, they have to talk.”
Prior to Wednesday’s 5-2 win against Leicester in the fourth round of the League Cup, United had won just one of their past eight games in all competitions.
Ten Hag won the League Cup and FA Cup during his spell at Old Trafford but the club have not won the Premier League since 2013, in Alex Ferguson’s last season in charge.
Ferguson won the Premier League title 13 times but since his departure five permanent managers have come and gone without adding to the club’s 20 top-flight titles.
Van Nistelrooy said Thursday he was “motivated” to help turn United’s season around and wants to stay at the club as he prepares the players for a high-profile match against Chelsea on Sunday.
Asked if it is his expectation that he will remain as an assistant under the new United boss Van Nistelrooy, a former PSV Eindhoven manager, said: “We will see but it’s a contract situation that I’m in, and my desire to help the club go forward.
“So I can speak to you about my side of this story, and after that, when the new situation is occurring, when the new manager is signing and conversations take place, we have to see how things develop.”
