The writing had seemingly been on the wall for Solskjaer since the humiliating defeats by local rivals Liverpool and Manchester City with the Hornets ultimately delivering the final blow.
His departure comes with United seventh in the table after Saturday’s defeat having won only one of their last seven Premier League games, while Solskjaer won 54.2 per cent of his games in charge.
That is lower than predecessor Jose Mourinho’s 58 per cent but a better win rate than United’s other permanent managers in the post-Sir Alex Ferguson era, David Moyes (52.9 per cent) and Louis Van Gaal (52.4).
Solskjaer’s initial spell in caretaker charge after Mourinho’s dismissal was an overwhelming success, with 14 wins from 19 games making it a foregone conclusion he would be given the job on a permanent basis.
They scored 12 goals in his first three games in temporary charge, won the first eight and beat Tottenham and Arsenal along the way, and had 10 wins and a draw in his first 11 before Paris St Germain inflicted a first defeat.
An astonishing 3-1 win in the return leg of that Champions League tie saw United through on away goals and was the third straight win with three goals scored as United netted 40 and conceded only 17 in the 19-game spell – though curiously, Solskjaer’s eventual long-term appointment came after back-to-back defeats to Arsenal in the league and Wolves in the FA Cup.
Having taken the job full time, Solskjaer lost five of his next seven games to Wolves, this time in the league, Barcelona in both legs of the Champions League quarter-final, Everton and Manchester City.
That set the tone for around two and a half years of inconsistent results and frequent questions over his future in the role.
United finished third and then second in the league under his stewardship and also reached last season’s Europa League final, losing on penalties to Villarreal.
They started this season with 13 points from their first five league games but their win rate dipped below 50 per cent, to seven from 16, after the humiliating defeats to Liverpool, City and Watford.
They have conceded 16 goals in their last six league games and have kept only two clean sheets in any competition all season, in league wins over Wolves and Tottenham.