First-half goals from Jamal Campbell-Ryce and Lewin Nyatanga and a late header from Jon Macken were enough to give the FA Cup semi finalists another season in the second tier.
Campbell-Ryce gave Charlton an early warning with a 20-yard effort but Nicky Weaver made a comfortable save.
But it was the winger who provided the early boost the home side needed with an emphatic opener for his fourth goal of the season.
First Macken spun cleverly near the edge of the area but his shot cannoned off a defender for Campbell-Ryce whose first shot was blocked but, when it fell back to him, he made no mistake drilling in the low angled shot.
Three minutes later Barnsley could have doubled their advantage. Macken did well again shielding the ball and producing a neat accurate cross from the byline but Kayode Odejayi's header was straight at Weaver.
Charlton, with nothing at stake, were close to levelling when 16-year-old Jonjo Shelvey - the club's youngest ever player - slipped an astute ball for Darren Ambrose but his shot on the half-volley was a fraction wide.
As Charlton found their feet, Luke Varney cut in from the right and fired a low shot wide before Shelvey almost scored on his debut. He pounced on a loose ball in the area as Barnsley tried to clear a corner and drilled an excellent shot that Rob Kozluk headed off the line.
But Barnsley were quick to break again and another stinging effort from Campbell-Ryce brought a full-stretch save from Weaver.
And a second goal from the home side settled any lingering nerves around Oakwell. Bobby Hassell chased a lost cause to produce a short cross, and when Dennis Souza headed into the danger area, Nyatanga was on hand to finish off with a close-range shot.
Only a last-ditch block stopped Barnsley claiming a third goal when Brian Howard's corner was headed goalwards by Souza and then Odejayi's shot was blocked.
Striker Macken headed in the third five minutes from time after a brilliant cross from Marciano van Homoet.
And only the bar denied Hassell when he dipped a quick free-kick over the keeper and hit the woodwork.