Goals from Adel Taarabt and Tommy Smith secured victory, meaning they cannot be caught by third-placed Cardiff and should have booked their place in the top flight as well as clinching the npower Championship title.
Neil Warnock and his coaching staff all embraced on the touchline but the celebrations will be slightly muted with the club now nervously awaiting the outcome of next week's FA hearing into the transfer of Argentinian midfielder Alejandro Faurlin.
Their fans shrugged off fears of a points deduction and hailed their side as 'champions' but Watford's fans responded by warning them 'you're gonna lose in the play-offs'.
The wheels fell off Rangers' promotion push at Vicarage Road last season courtesy of a 3-1 defeat and a dressing-room bust-up which led to the departure of Jim Magilton as manager. Their cause was not helped this time around when goalkeeper Paddy Kenny was injured in the warm-up, while Fitz Hall's hamstring lasted only 20 minutes longer.
However, Taarabt's 19th goal of the season and Smith's injury-time strike means only the FA can deny them top-flight football for the first time in 15 years.
Source: PA
Source: PA