The Pilgrims started brightly in the West Country sun and took the lead with a well-executed header by Gary Sawyer on 12 minutes.
Barnsley took time to recover and almost fell further behind to an Alan Judge rocket, before Adam Hammill levelled with a neat drive on 34 minutes. Jamal Campbell-Ryce sealed all three points with a low shot early in the second half.
The Tykes arrived at Home Park knowing a draw would be enough to keep them in the second tier of English Football and send Norwich City down to League One.
The large contingent of travelling supporters were hoping the already-safe Pilgrims had an eye on the summer holidays, but the opening ten minutes were completely dominated by the hosts.
That dominance reaped deserved reward when Sawyer met a Paul Gallagher corner at the near post and flicked a deft header beyond goalkeeper Luke Steele and into the top corner.
Steele, however, came out on top in his next duel, producing a remarkable save to tip Judge's thunderous volley onto the crossbar.
It was a gratefully accepted reprieve for the Tykes and they swept up the other end to grab a vital equaliser. Jon Macken was the instigator, cushioning a clever header into the path of Hammill, who cracked an instant shot into the bottom corner.
Barnsley came out firing after the interval and, with Norwich losing their must-win game at Charlton, Campbell-Ryce pounced to break Canaries hearts.
Macken was again involved in the approach play, holding off Marcel Seip before teeing up Cambell-Ryce for an easy finish.
Argyle lacked the urgency to fight a way back into the match and Barnsley were content to play out the final minutes of a turbulent season.
Well done to the Tykes. On the day they needed a result, they delivered.