Slavisa Jokanovic’s side had moved to the brink of reaching the top-flight with a 2-0 win at Brighton earlier in the day, yet it seemed like the Championship leaders would be made to wait for promotion by the results of the chasing pack.
But fourth placed Norwich conceded an equaliser in a 1-1 draw at Rotherham and third placed Middlesbrough slumped to a 4-3 defeat at Fulham after conceding a last-minute goal.
That was enough to seal Watford’s return to the Premier League after an eight-year absence with one match remaining and they will be crowned Championship winners if second placed Bournemouth lose to Bolton on Monday.
It was the perfect end to a day that started promisingly for the Hornets as they eased to a fifth successive victory thanks to goals from Troy Deeney and Matej Vydra.
Deeney broke the deadlock with his 21st goal of the season in the 29th minute.
A cross by Odion Ighalo was only half cleared by defender Greg Halford and the ball fell kindly for Deeney to smash home.
Chris O’Grady came close to grabbing an equaliser for Brighton six minutes from time when he headed narrowly wide at the near post.
But Deeney slipped in Vydra for his 15th goal of the season to wrap up a victory that secured promotion just hours later.
“It was a relief. Brighton pressed at the start and the end of the game, so it was an important second goal,” former Chelsea midfielder Jokanovic said of the celebrations that greeted Vydra’s goal.
“It’s very important for us to keep going for 46 games. I don’t have any plans for tonight and tomorrow. I will be preparing for the next game.”
Watford’s players and fans were able to start popping the champagne corks thanks to the efforts of Fulham and Rotherham.
– Fatal blow –
Middlesbrough’s hopes of automatic promotion were dealt a potentially fatal blow by Fulham striker Ross McCormack’s hat-trick at Craven Cottage.
Aitor Karanka’s side trailed 2-0 and then 3-1, following George Friend’s dismissal, but they somehow clawed themselves back to 3-3 with one minute to go.
That would have been enough to deny Watford promotion for another week, but they rolled the dice for a winner when goalkeeper Dimitrios Konstantopoulos went up for a corner that was cleared, allowing McCormack to find the net at the other end in stoppage-time.
McCormack’s winner came minutes after the other result Watford needed was confirmed at the New York Stadium.
Norwich had been reduced to 10 men following Lewis Grabben’s first half dismissal, yet they still took the lead through Gary Hooper’s 59th minute strike.
But fourth bottom Rotherham’s need for the points was just as great as they try to avoid relegation following a three-point deduction for fielding an ineligible player.
And Steve Evans’ side equalised in the 86th minute through Jordan Bowery to complete Watford’s joy.
Bournemouth can now effectively clinch promotion with a win over Bolton on Monday as that would leave them three points clear of Middlesbrough with a vastly superior goal difference ahead of next weekend’s final round of fixtures.
Fifth placed Ipswich are on course for a play-off place after beating Nottingham Forest 2-1, while Derby hold the final play-off berth following their 3-3 draw at Millwall.
Brentford, 2-0 winners at Reading, and Wolves, who won 1-0 at Wigan, can also still snatch a play-off berth on the final day.
Millwall and Wigan will be relegated to League One if Rotherham win their game in hand against Reading on Tuesday.