The club confirmed on Tuesday morning that Sir Alex Ferguson's successor had "left the club" after less than a season in charge.
Moyes endured a miserable time in charge, with Sunday's 2-0 loss at his former club Everton the latest setback.
It is understood Moyes was sacked by vice-chairman Ed Woodward during a meeting at the club's Carrington training ground this morning shortly after 8am.
The club had previously backed their manager despite a series of dreadful results, but Sunday's defeat at Goodison Park proved one too many.
With a £150million spending spree planned for the summer the club's owners, the Glazer family, wanted to make sure they had the right man at the helm to bring success back to Old Trafford.
A statement from the club, released at 8:30am, read: "Manchester United has announced that David Moyes has left the club.
"The club would like to place on record its thanks for the hard work, honesty and integrity he brought to the role."
It is understood that long-serving midfielder Ryan Giggs will be announced as interim manager later on Tuesday.
There will be no shortage of takers when it comes to seeking a successor for Moyes, who turns 51 this Friday.
Louis van Gaal is among the front runners. The former Barcelona manager has an impressive CV and will be available this summer when he leaves his post as Holland coach.
Borussia Dortmund coach Jurgen Klopp is among the fans' favourites to take over, but the club are understood to favour other candidates.
Diego Simeone is a highly regarded figure in European football after taking Atletico Madrid to the top of the Spanish league and into the semi-finals of the Champions League.
However, many fans would like to see Giggs take the post on a long-term basis, despite his lack of managerial experience.
Moyes slipped into United's base in Carrington un-noticed on Tuesday morning.
Succeeding Sir Alex Ferguson, who won 13 league titles during his time at the club, was always going to be difficult, but few expected this season to have gone so badly.
The list of unwanted records broken by Moyes is as embarrassing as it is long. United are guaranteed to end the season with their worst points total in Premier League history, they have failed to qualify for the Champions League for the first time in almost two decades while Moyes' home record is the worst of any United boss since 1978 when Dave Sexton was in charge.
The Red Devils are seventh in the Barclays Premier League with four matches to go, with Europa League qualification now also looking unlikely.
Moyes won 27, drew nine and lost 15 of his 51 games in charge.
The Scot was dogged by claims he was not up to the job ever since he took over last July.
Moyes had enjoyed 11 critically-acclaimed years at Everton, leading the club to five top-six finishes. The Toffees qualified for the Champions League for the first time under Moyes' stewardship - although they lost in the qualifying stages of the competition - and he also took the Merseyside club to the FA Cup final in 2009.
But all those achievements were small fry compared to what his predecessor achieved.
The enormity of the task in hand seemed to overwhelm Moyes from day one.
Moyes upset some within the club by bringing in his own coaching staff, while the likes of Rene Meulensteen, Eric Steele, and Mike Phelan departed.
Moyes also botched his first transfer window as United boss. The Scot pursued Barcelona's Cesc Fabregas when the Spaniard had no intention of leaving the SpaniSh giants.
Thiago Alcantara joined Bayern Munich ahead of United, while the club made a real hash of their attempts to sign Marouane Fellaini and Leighton Baines on the cheap.
United's bid of £28million for the pair was branded "derisory and insulting" by Everton.
Baines stayed and United ended up buying Fellaini for £27.5million when they could have bought him for £4million less had they acted quicker.
Moyes rarely looked comfortable in front of the cameras, and for that reason many felt Jose Mourinho, who left Real Madrid to rejoin Chelsea last summer, would have been a better option.