Quick-fire goals from Greg Halford, Simon Cox and Chris Cohen set The Reds on their way to their third win in four Championship games.
Substitute Jermaine Jenas got in on the goal-scoring act in the second half – his first Forest goal in more than a decade – to set the seal on a satisfying afternoon’s work.
Ex-Forest striker Marlon Harewood had given Barnsley the lead midway through the first half but Sean O’Driscoll’s men came roaring back in style.
The win lifted Forest into the top six in the Championship and extended their unbeaten run to five matches ahead of next Saturday’s Kids for a Quid game against Millwall at The City Ground.
O’Driscoll made one change to his starting line-up with Brendan Moloney coming into the back four in place of the injured Daniel Ayala.
New emergency loan signing Elliott Ward was named among the substitutes, alongside Dexter Blackstock, whose last-gasp goal had rescued a point at Blackpool in midweek.
A mistake by home defender John Stones presented Andy Reid with an early opportunity but the Irishman was unable to capitalise and fired straight at Ben Alnwick.
Forest went close in the 15th minute as a Halford free-kick caused panic in the home side’s area. Halford’s effort was charged down but Barnsley failed to clear and after Cohen’s goal-bound shot had been blocked Reid fired wide.
Billy Sharp should have given the visitors the lead moments later but planted his free header wide of the target from Reid’s first-time cross from the left.
But it was Barnsley who drew first blood – against the run of play. Jacob Mellis sent Harewood clear and the big striker calmly rounded Lee Camp before bagging the first goal of his Oakwell career.
Dan Harding made a vital clearance from under his own bar – with Matt Done lurking – as Barnsley looked to extend their lead.
But Forest deservedly levelled matters 10 minutes before half-time as Halford cut in from the right before trying his luck with a shot with the outside of his right foot, which took a deflection off Scott Wiseman that wrong-footed Alnwick.
The Reds were ahead just three minutes later as Cox grabbed his third league goal of the season by firing home from close range after Alnwick parried Sharp’s shot following a quick break down the right by the excellent Cohen.
Things went from bad to worse for shell-shocked Barnsley on the stroke of half-time as Cohen made it 3-1 with a shot from 25 yards out after good work down the left by Reid.
Forest started the second half in positive fashion and Cox came close to claiming a second of the afternoon in spectacular style. The Republic of Ireland international beat Alnwick to a Reid cross from the left and was then inches away from scoring with an audacious overhead kick.
Barnsley made three changes soon afterwards introducing Kelvin Etuhu, Tom Kennedy and Chris Dagnall as they looked to re-establish a foothold in the game.
Camp had to make a sprawling save to keep out a Kennedy free-kick and the Forest No. 1 also blocked from Etuhu at point-blank range.
Halford collected his fifth booking of the season which rules him out of the Millwall game, while Sharp could have put the result beyond doubt after latching on to Dan Harding’s long diagonal ball forward but dragged his shot wide.
Alnwick had to be alert to keep out a Sharp header from a Reid corner but it was Jenas, on as a sub for Majewski, who wrapped up the win 12 minutes from time.
Cox sent the England midfielder clear and Jenas provided a sublime finish by lobbing the on-rushing Alnwick.
The trip to Barnsley marked the end of Jenas’ initial one-month loan and Forest must now decide whether to extend stay at The City Ground.
O’Driscoll handed Ward his debut 10 minutes from time as The Reds eased to a convincing victory in South Yorkshire.
Camp, Halford (Ward 78'), Moloney, Collins (c), Harding, Gillett, Cohen, Majewski (Jenas 69'), Reid (Coppinger 80'), Cox, Sharp
Subs not used: Darlow, McGugan, Greening, Blackstock.
Scorers: Halford 35', Cox 42', Cohen 45', Jenas 77'
Booking: Halford 66'
Alnwick, Stones, Foster, Wiseman, Golbourne, Dawson (Dagnall 54'), Perkins, Done (Kennedy 51'), Cywka (Etuhu 51'), Harewood, Mellis
Subs not used: Steele, Hassell, McNulty, Rose
Scorer: Harewood 24'
Referee: Kevin Friend
Attendance: 10,186 (Away 2,217)