A statement from the club said: “The club would like to thank Jose for his work during his time at Manchester United and to wish him success in the future.
“A new caretaker manager will be appointed until the end of the current season, while the club conducts a thorough recruitment process for a new, full-time manager.”
The news comes two days after United’s 3-1 Premier League defeat at Liverpool, which left them 19 points behind the table-topping Reds in sixth place, and 11 points off the top four.
Mourinho took charge at United, succeeding Louis van Gaal, in the summer of 2016 and they won the Europa League and League Cup in their first season under the Portuguese.
The Red Devils then finished second in the Premier League last term, before making a troubled start to this season, winning only seven of 17 league games and being knocked out of the League Cup at home by Championship club Derby County.
Former Real Madrid boss Zinedine Zidane has been heavily linked with United since his summer departure from the Spanish club, who he guided to the Champions League title in each of the last three seasons.
Another man who has been frequently spoken of as a potential United manager is Tottenham’s Mauricio Pochettino.
The likes of Didier Deschamps, who led France to World Cup glory over the summer, and ex-Red Devils defender Laurent Blanc could also be in the frame.
Former United defender Gary Neville believes the Red Devils should try to bring in Pochettino as Mourinho’s replacement, describing the Argentinian as the “ideal candidate”.
He said: “I said last season that the next manager of Manchester United should be Mauricio Pochettino.
“When I look at the values of Manchester United, you look at Mauricio Pochettino’s belief in young players at Southampton and with Tottenham. You look at his performance levels and the style of play, the way in which he carries himself at all times, publicly and in private.
“I’ve been fortunate enough to spend two or three days at Tottenham’s training ground and to me he just feels like the most ideal candidate.”
“Manchester United have tried managers that have won European Cups, they’ve tried managers that have won multiple leagues, they’ve tried managers that have, to be fair, had that solid grounding in the Premier League,” Neville said.
“They need someone who meets the three key principals of that football club: the promotion of youth, entertaining football and to win football matches.
“People suggest he hasn’t won a trophy yet at Tottenham but with a net spend of minus £29million or something over the last four years, I’m not sure he could have done more.
“I do think he is the person who is the outstanding candidate.”