The Rams looked set to do east midlands rivals Nottingham Forest a huge favour after Chris Porter's second goal of the season handed them a 49th-minute lead against a Baggies side who looked jaded after their FA Cup exploits in midweek.
But Brunt grabbed the game by the scruff of the neck and grabbed a 10-minute brace to turn the encounter on its head, before Simon Cox put a gloss on the scoreline with a late third although it was anything but comfortable for the hosts.
The victory, made all the sweeter for Albion by Forest's 3-0 defeat at Leicester, ended a run of four games without victory in all competitions.
Derby, meanwhile, remain consistently inconsistent and continue to slug it out in the lower-mid echelons of the table.
There was a lively start to affairs at The Hawthorns with action coming at either end.
And the first moment of controversy came with just minutes on the clock as Gabriel Tamas seemingly barged over Stephen Pearson in the penalty area as the two went shoulder to shoulder, but referee Phil Crossley saw nothing wrong.
Luke Moore then saw his clever backheel deflected narrowly wide at the other end but, with the frantic opening having disappeared, there was very little quality on show from either side.
Robert Koren should have handed Albion the lead midway through the half but blazed well over when in a good position with just Stephen Bywater to beat.
The hosts were looking more likely to break the deadlock and Robbie Savage had to block Koren's goalbound shot, but Pearson then came within inches of a 40th-minute breakthrough in what was Derby's best chance of the half.
But, despite loud claims from the home faithful for a late penalty, the opening 45 minutes contained very little to shout about.
Derby started on the front foot after the restart and soon got their reward for a well-worked move.
The ball was recycled back to Savage who split the home defence with a great pass that found its way to Porter and he did the rest.
Northern Ireland international Brunt was presented with a great chance to level matters almost immediately but his header was caught by Bywater.
But it could and should have been all over soon after as on-loan Arsenal man Gilles Sunu blazed a gilt-edged cut back over the bar from six yards.
Derby were by the far the dominant force as the second half wore on with Albion at sixes and sevens.
But out of nowhere, the Black Country club were level in the 67th minute courtesy of a great left-footed strike from Brunt on the edge of the area that flew into the bottom corner.
The leveller inspired Albion and Brunt completed the turnaround 10 minutes later, firing over the line from close range as the ball pinged around in the penalty area from Graham Dorrans' corner.
Cox then made it 3-1 with a well-taken finish from 18 yards seven minutes from time.