The Scotland international, who was on Tuesday the subject of a £4million bid from West Ham, has been the heartbeat of Albion's immediate return to the Premier League and it was apt that he popped up to write the final chapter in their season.
Albion were facing their first defeat at The Hawthorns since early January and the first time they had failed to find the net in 26 league games.
But both sets of fans were partying at the final whistle, with the away contingent left celebrating Yorkshire rivals Sheffield Wednesday's relegation from the Championship.
Hugo Colace had looked to be the matchwinner for the Tykes, creeping in unmarked to prod home after West Brom's defence had been caught napping.
The result left West Brom on 91 points - a club record in a single season - but not enough to eclipse the 92 recorded by Leicester in 2002/03, the highest ever recorded for the runners-up in England's second tier.
The encounter naturally had a typical end-of-season feel about it in chilly conditions not associated with the final weekend of the season.
And a tendency from both sides to stand off and not commit to challenges, likely due to the dead-rubber nature of the match, led to an open contest from the off.
Martin Devaney lashed wide for the Tykes before Chris Brunt whistled an effort inches off target at the other end, while neat interchange in and around the area was often stifled due to last-ditch tackling or wayward shooting.
The two teams were more than comfortable playing a passing game as a Mexican wave swept around The Hawthorns midway through the first half, although goalscoring opportunities had quickly become few and far between.
Steven Reid and Chris Brunt came close to a breakthrough from Dorrans' 34th-minute corner before the midfielder picked up the loose ball and saw his shot blocked by the arm of ex-Albion stalwart Darren Moore but, as the half-time whistle sounded, neither goalkeeper had yet to make any real save of note.
The wasteful finishing continued after the restart, ensuring a repeat of West Brom's resounding 7-0 triumph over the Tykes on the final day of the 2006/07 season was extremely unlikely.
Iain Hume blasted high and wide before Roman Bednar followed suit having found himself in the clear when centre-back Ryan Shotton mis-judged his interception.
But Colace showed it could be done in the 59th minute when, with the home defence sleeping, he popped up unmarked to calmly side-foot home Jacob Butterfield's inswinging free-kick from close range.
Luke Steele produced a fine save to tip Robert Koren's goalbound drive over the bar as Albion went in search of an equaliser.
The hosts significantly upped the tempo after Barnsley's opener with Steele far busier between the sticks, although he only had to watch Koren's header drift harmlessly wide when the Slovenia captain should have done better.
Jonathan Macken should have put the result beyond doubt but sent his header wide - providing the opportunity for an unmarked Dorrans to level matters and spark a celebratory pitch invasion.