Regis Le Bris’ side trailed to Tyrese Campbell’s first-half goal at Wembley, but Eliezer Mayenda equalised in the closing stages before Watson delivered the priceless last-gasp winner.
It was an astonishing twist to the single richest match in world football as Sunderland recovered from a sluggish start to hit the jackpot with a promotion worth an estimated £200 million (US$270 million) in increased revenue.
Watson’s moment ensured Sunderland fans can look forward to renewing hostilities with bitter rivals Newcastle next season.
Sunderland’s return to the Premier League for the first time since 2017 comes after a dark period that included a four-season spell in the third tier.
The Black Cats suffered five successive defeats coming into the play-offs, but they dug deep to reach the top-flight in the most remarkable style.
With a penalty shoot-out just seconds away, Dan Ballard’s last-gasp extra-time header sealed a 3-2 aggregate success in the semi-final second leg against Coventry.
They looked down and out with only 14 minutes left at Wembley before the stunning denouement.
Promotion completed an impressive rise for Le Bris, a 49-year-old Frenchman who arrived at the Stadium of Light last year after suffering relegation from Ligue 1 with Lorient
United are still without a win at Wembley in 100 years and have now endured four Championship final defeats among 10 failed attempts to win promotion via the play-offs.
United had finished in third place in the table, 14 points clear of fourth-placed Sunderland in the regular season, but that gap proved irrelevant.
Sunderland keeper Anthony Patterson made a brilliant save in the second minute, diving to his left to claw Kieffer Moore’s header off the line.
Patterson’s stop conjured memories of Jim Montgomery’s incredible save to help Sunderland shock Leeds in the 1973 FA Cup final.
Injured trying to stop Moore’s header, Sunderland captain Luke O’Nien was forced off with a dislocated shoulder that left him writhing in pain.
United deservedly took the lead in the 25th minute.
Ben Hamer showed why he was voted Championship Player of the Year with a perfectly weighted pass to Campbell, who guided a composed finish over Patterson from 12 yards.
It was a poignant moment for the 25-year-old approaching the first anniversary of the death of his father – former Arsenal and Everton striker Kevin Campbell.
Harrison Burrows thought he had doubled United’s lead nine minutes later, but his strike was disallowed for offside against Vini Souza after a VAR check.
United substitute Andre Brooks barged through on goal after the interval, but Patterson stuck out his foot to make a superb save.
It proved a costly miss, as Mayenda hauled Sunderland level with only their second shot on target in the 76th minute.
Patrick Roberts’ pinpoint pass reached Mayenda just inside the area, and he punished United’s sloppy marking with a fierce finish into the roof of the net.
O’Nien, his shoulder in a sling, sprinted off the bench to embrace Mayenda, waving his one healthy arm in jubilation.
That celebration was only the precursor to the ecstatic scenes sparked by Watson five minutes into stoppage-time.
Seizing on Moore’s loose pass, Watson drove towards the edge of the United area and curled a low shot into the bottom corner past Michael Cooper’s fatally slow dive.
Watson is due to join Brighton in the close-season, and his thrilling winner was the perfect farewell gift, ensuring Sunderland will join the 19-year-old among English football’s elite. (AFP)
