Nothing less than a victory would have sufficed on an afternoon of high-stakes at Oakwell, and the Reds were just a couple of minutes away from League One after spurning a host of chances throughout the game.
But Schmidt popped up to be the unlikely hero in the most dramatic circumstances imaginable, and Barnsley fight to live another day.
The fate of Forest goes down to the final round of fixtures too, as they lost the point required to secure their place in the play-offs.
Story of the match
Barnsley dominated possession in the first half and had most of the chances. Jordan Smith was forced into two early saves, denying Alex Mowatt and then Luke Thomas.
Lewis Grabban only had the chance to show very brief glimpses of his quality, firing one low shot wide from a difficult angle, while Tobias Figueiredo was the only other Forest player to go close but was blocked off following a scramble.
Thomas, impressing in the hole behind the front two for Barnsley, came agonizingly close when his sweet connection with Kilian Ludewig’s cross clipped the top of the bar. Mowatt also went close from outside the box, stroking an effort narrowly wide.
Grabban attempted to convert a Tiago Silva cross with an audacious flick but couldn’t aim it on target, while the last chance before the break saw Jacob Brown played through on goal by Conor Chaplin for the hosts, only to fail to sort his feet out before Smith had come out of his goal to block.
The second half turned into a more open and competitive affair, with both sides getting the ball into dangerous positions more regularly and scrambling defence required from both backlines.
Fresh impetus from the bench gave Forest some extra spark but Barnsley were coming closest to finding the goal. Marcel Ritzmaier’s deflected strike came back off the post, while Joe Worrall had to make a vital block from Matty Wolfe after Brown poked the ball towards the back post.
Barnsley continued to push, effectively playing with five forwards in the final minutes, and all looked lost when Chaplin twice had efforts blocked.
But they would not give in, and they won the game in remarkable fashion as substitute Schmidt turned and finished from the middle of the box to take the relegation fight to the final day.
Barnsley fight to the end
Barnsley have been written off all season, and when they needed a goal in the final couple of minutes having scored just four in the eight matches since the restart, it looked like there was no way they could possibly turn it around.
And yet where there’s a will, there’s a way. Nobody could accuse them of not trying hard enough, and those efforts finally paid off as Schimdt stroked in the winning goal.
They will still be up against it on the final day, heading to promotion-chasing Brentford needing a win and several other results to go their way, but after this drama only a fool would rule them out.
Forest can forget about a back five
A sceptic might suggest he was happy to play for the point, but with a play-off place still almost certain and some better form badly needed, this was a tactical experiment from Sabri Lamouchi, and one which did not reap rewards.
Forest have succeeded this season with a direct, counter-attacking style of play but this formation, best described as a 5-2-1-2, was totally ill-suited to their style. Without the explosive qualities of Joe Lolley or Sammy Ameobi, they had almost no outlet and barely had a sniff in the attacking third for most of the match.
Man of the match: Callum Styles (Barnsley)
Styles has impressed in recent matches for Barnsley, whether in midfield or at left wing-back like today, and he was solid and composed in defence all game while offering threat going forward.