Hull have been promoted to the top flight for just the second time in their 109-year history on a dramatic afternoon at the KC Stadium in which they were forced to wait 20 minutes before their fate was determined.
Hull were held to a 2-2 draw at home to Cardiff as a late goal for the champions denied them the chance to keep their fate in their own hands.
Former Hull loanee Fraizer Campbell had given Cardiff the lead before the break before the hosts turned it around with two goals in five minutes through Nick Proschwitz and Paul McShane.
Andrew Taylor was then sent off before Proschwitz had a penalty, which would surely have guaranteed promotion, saved. Instead, Nicky Maynard earned Cardiff a share of the spoils from the penalty spot although matters at Vicarage Road would ultimately transpire in Hull's favour.
That allowed Watford an opportunity to sneak ahead as injury caused severe delay to their game against Leeds United, but as they sought a winner they conceded a late goal to lose 2-1, confirming Hull's place in the Premier League.
Watford, without Manuel Almunia due to an injury in the warm-up, saw replacement goalkeeper Jonathan Bond taken to hospital after a sickening collision. Watford's rookie third-choice keeper Jack Bonham, who was not even in the squad half an hour before kick-off, came on for his professional debut.
Dominic Poleon gave Leeds the lead, but Almen Abdi curled in a superb first-time shot to level matters deep into first-half stoppage time.
Watford saw Troy Deeney red-carded after 60 minutes, but the news from the KC Stadium inspired the ten men towards a late charge. However, as the Hornets applied the pressure, Ross McCormack broke away down the other end and grabbed a late winner for Leeds.
At the other end, Peterborough were relegated after losing 3-2 at Crystal Palace.
Palace secured fifth with goals from Glenn Murray, Kevin Phillips and Mile Jedinak. Peterborough had led twice through Lee Tomlin and Nathaniel Mendez-Laing but their efforts were to prove in vain.
Wolves, whose Championship status looked incredibly fragile before the final round of fixtures, also went down following a 2-0 defeat at Brighton.
A Kazenga LuaLua double after nine and 39 minutes earned Brighton the three points to give them fourth place and a play-off spot as Wolves joined Posh and Bristol City in League One.
Barnsley led twice at Huddersfield and despite being pegged back did enough to stay up with a 2-2 draw.
Chris O'Grady and Jason Scotland twice put Barnsley in front but Jermaine Beckford and James Vaughan scored the equalisers. With news of Peterborough's defeat to Palace, both teams took their foot off the gas to ensure both teams' survival.
Sheffield Wednesday made sure of their status with a 2-0 home win over Middlesbrough thanks to goals from Steve Howard and Leroy Lita, while Millwall beat the drop despite a late Conor Sammon goal giving Derby a 1-0 win.
Leicester sneaked into the play-offs with a 3-2 win at Nottingham Forest with goals from Matty James, Andy King and Anthony Knockaert.
Forest, who scored through Simon Cox and Elliott Ward, lost out along with Bolton, who were held 2-2 at home by Blackpool.
Matt Phillips and Ludovic Sylvestre put Blackpool in charge before Chris Eagles and Craig Davies gave the home side hope but it was in vain.
Charlton defeated already relegated Bristol City 4-1 with Yann Kermogant (2), Jonathan Obika and Johnnie Jackson getting the goals, Bobby Reid scoring for the Robins.
Information from the Press Association was used in this report