A scrappy encounter at a blustery Vicarage Road on Easter Monday looked to be heading towards stalemate until Graham lashed home a superb 25-yard effort - but Brunt popped up to spoil the party and head home from close range after six minutes of injury time had been shown.
Malky Mackay's side, who had seen Jon Harley sent off for a second bookable offence minutes prior to their opener, are now out of the bottom three by just goal difference alone after results elsewhere.
Mackay will also be seriously concerned by what appeared to be a season-ending leg injury for Manchester United's on-loan youngster Tom Cleverley.
Albion went into the game knowing victory for them combined with a draw or defeat for third-placed Nottingham Forest at home to Cardiff would secure their immediate return to the Premier League.
And although automatic promotion was not secured today, it does seem to be a case of if and not when for the Black Country club.
Roberto Di Matteo was able to rotate his ranks and call upon established duo Giles Barnes and Roman Bednar, while Gianni Zuiverloon also came in at right-back for the injured Steven Reid.
In stark contrast, out-of-sorts Watford were without the key trio of Henri Lansbury, Heidar Helguson and Martin Taylor due to suspension and injury.
And despite Albion's impending promotion party, the hosts were quick to remind the visitors of their desire for all three points at the other end of the table.
Baggies keeper Scott Carson was forced to make a fine point-blank save from Adrian Mariappa before Mackay saw his selection problems worsen with the early loss of Lloyd Doyley to injury.
West Brom were struggling to get into the encounter, with their passing game not helped by a bobbly surface.
Although Di Matteo's side steadily gained a foothold as the first half wore on without really posing a serious threat to Hornets stopper Scott Loach.
A fiery scuffle involving Watford skipper John Eustace and Graham Dorrans, which was joined by a host of other players, raised temperatures inside Vicarage Road.
But, with Will Buckley firing off target when in a good position, the half-time scoreline remained goalless.
The first half-chance after the restart fell to Mariappa, who stung the gloves of Carson with a rasping 30-yard drive in the 53rd minute.
At the other end, Bednar went down in the area under pressure from substitute Jay DeMerit but his appeals were waved away.
Robert Koren then saw his effort well blocked by Dale Bennett as Albion, minus the injured Zuiverloon, started to impose themselves.
As well as Doyley, Watford had also lost Buckley to injury when their survival hopes suffered a real blow as United loanee Cleverley was stretchered off with his leg in a splint.
Matters went from bad to worse for the hosts as Harley saw red for a second bookable offence in the 79th minute.
But just minutes later Graham popped up to send the home crowd wild with a marvellous opener from distance which looked to have settled matters.
That was until, with James Morrison having already missed a glorious chance to level, Brunt headed home from six yards with 95 minutes on the clock.