Hull City have been promoted to the Premier League following a 2-2 home draw against Cardiff City.
Watford, who started the day in third place in the Championship table, lost at home to Leeds and missed the chance to go up to English football's top division automatically.
Gianfranco Zola's team will now compete in the play-offs at the end of the season.
Wolverhampton Wanderers have been relegated to League One after losing 0 – 2 to Brighton.
Click here for the latest football updates on the final day of the Championship as teams aim for promotion and to avoid relegation.
Ahead of their march against Cardiff City which could see Hull City end their three-year exile from the Premier League if they win, the club has tweeted:
The club need to match Watford's result at home to Leed to ensure second place automatic promotion.
Watford could return to the Premier League today.
The Hornets are third in the Championship, a point off the promotion places behind second-placed Hull.
Quite simply, if Watford get a better result than Hull, they'll go up.
The fixtures are in Watford's favour as Hull face the already-crowned champions Cardiff, while the Hornet's opponents Leeds have been struggling in 16th.
Watford manager Gianfranco Zola has said that an entire year's work now comes down to this one game.
Even if they can't do better than Hull tomorrow, they'll still have a chance of ending their six year exile from the top flight via the play offs.
Both games kick off at 12:45.