Andy Ritchie's side, second from bottom at the start of play, had drawn first blood but conceded two goals in two minutes just before the break to leave themselves with a mountain to climb.
Yet the introduction of former Manchester United striker Daniel Nardiello as a second-half substitute helped pave the way for a splendid recovery which ultimately secured three points in the Championship survival stakes.
Leeds had been the better side in the opening minutes of the first half, with new boss Dennis Wise having given a starting slot to Barnsley-born striker Geoff Horsfield.
And it was the visitors that almost took the lead in the 12th minute when a lovely low cross from David Healy narrowly evaded the lunging Robbie Blake at the far post.
It was a rather tense, scrappy start to a crucial clash and Horsfield headed wide in the 13th minute from a good position while at the other end Barnsley's lively winger Michael McIndoe saw a fierce volley deflect wide.
Barnsley eventually broke through on the half-hour mark following a short free-kick. Brian Howard played the ball out wide to McIndoe who delivered a deep cross into the Leeds box, and when on-loan keeper Graham Stack failed to punch sufficiently clear, Martin Devaney volleyed through a crowd of players and into the net.
But Leeds turned the tables with two goals in as many minutes just before half-time.
The leveller arrived on 41 minutes when Blake's corner found Shaun Derry unmarked and his close-range header gave Barnsley's Irish keeper Nick Colgan no chance.
Seconds later Marc Richards spurned a glorious chance to put Barnsley back in front, volleying over from six yards, and Leeds made him and the home side pay by snatching the lead, Blake getting the better of Paul Reid in the box and drilling home right-footed.
But it was Barnsley that raised the tempo in the second half, particularly after the introduction of Nardiello. He made an immediate impact and suddenly the Leeds defence was under pressure.
Barnsley drew level in the 62nd minute when McIndoe came inside and drilled a low left-footer beyond Stack from the edge of the box.
Just four minutes later McIndoe was only inches away with a great volley on the run, before Nardiello's excellent work in the box teed up Howard 14 minutes from time and his rare right-footer beat Stack for what proved to be the winner.
Leeds looked deflated and Barnsley could have even added to their tally, with Nardiello hitting the post with an audacious lob and then testing Stack with a meaty drive.