The 40-year-old's appointment in November 2024 brought much hope and excitement to Old Trafford, with the highly-rated Sporting Lisbon coach succeeding Erik ten Hag on a deal until 2027.
But Amorim's reign has seen more lows - and press conference soundbites - than highs, including overseeing a worst top-flight campaign in 51 years as United slumped home 15th in the Premier League.
May's costly Europa League final loss to Tottenham compounded that and the club have wielded the axe with the Red Devils sixth in the standings following Sunday's 1-1 draw at rivals Leeds.
Darren Fletcher, who currently works as Under-18s coach, will take charge for Wednesday's Premier League match at struggling Burnley and could also oversee Sunday's FA Cup tie against Brighton.
The 41-year-old academy graduate made 342 first-team appearances for the Red Devils and has held a number of roles at since returning to the club in 2020.
The club hierarchy is understood to be weighing up their options, although it has been reported a caretaker could be appointed for the rest of the campaign before naming Amorim's permanent successor in the summer.
"Ruben Amorim has departed his role as head coach of Manchester United," the Premier League club said in a statement on Monday morning.
"Ruben was appointed in November 2024 and led the team to a UEFA Europa League final in Bilbao in May.
"With Manchester United sitting sixth in the Premier League, the club's leadership has reluctantly made the decision that it is the right time to make a change. This will give the team the best opportunity of the highest possible Premier League finish."
Amorim was fired just 19 hours after making a string of eye-catching comments at Elland Road, where he stressed he was United's manager rather than "just the coach" having hinted at frustration behind the scenes on Friday.
The Portuguese told the scouting department and sporting director "to do their job" during a blockbuster end to a post-match press conference that saw him raise major doubts over his future.
Club sources have told the Press Association that the decision to change managers was due to the lack of evolution and progress over his 14-month reign rather than a power struggle.
United were under the impression that Amorim would look to develop a more proactive, attacking style after implementing his well-documented 3-4-3 structure, but that did not come to pass.
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