The United hierarchy believed Solskjaer had earned the chance to turn around his side's slump, but the chastening nature of Saturday's defeat made it clear to them change was needed.
Ole Gunnar Solskjaer has been sacked as Manchester United manager after an "embarrassing" 4-1 defeat at Watford.
United have confirmed Solskjaer's assistant Michael Carrick will be placed in temporary charge, with the club also revealing their intention to appoint an interim manager until the end of the season.
Solskjaer signed a new three-year deal in July but leaves after overseeing five defeats in their last seven Premier League matches - a run which sees them 12 points behind leaders Chelsea.
The Old Trafford hierarchy had ignored increasingly vociferous calls to relieve Solskjaer of his duties in the wake of a humiliating 5-0 loss to rivals Liverpool and a 2-0 derby defeat to Manchester City in early November.
But his position was discussed by United officials on Saturday evening following the crushing defeat at Vicarage Road, before the announcement of his dismissal followed on Sunday morning.
A club statement said: "Manchester United announces that Ole Gunnar Solskjaer has left his role as manager.
"Ole will always be a legend at Manchester United and it is with regret that we have reached this difficult decision. While the past few weeks have been disappointing, they should not obscure all the work he has done over the past three years to rebuild the foundations for long-term success."
The United hierarchy believed Solskjaer had earned the chance to turn around his side's slump, but the chastening nature of Saturday's defeat made it clear to them change was needed.
Following a second-placed finish in the Premier League last season and the summer signings of Cristiano Ronaldo, Raphael Varane and Jadon Sancho, United chiefs expected to see further progress this campaign.
The club are satisfied Solskjaer has left them in a far stronger position than when he took over in December 2018, with their recent appointments of Darren Fletcher as technical director and John Murtough as football director considered to be crucial in minimising the disruption of a mid-season managerial change.
United added: "Ole leaves with our sincerest thanks for his tireless efforts as manager and our very best wishes for the future. His place in the club's history will always be secure, not just for his story as a player, but as a great man and a manager who gave us many great moments. He will forever be welcome back at Old Trafford as part of the Manchester United family."
Solskjaer was booed by a number of the United fans in the away end at full time at Watford, although midfielder Bruno Fernandes appeared to try to redirect their frustration towards the players.
Goalkeeper David de Gea labelled the defeat "embarrassing" and "unacceptable".