Jason Scotland's second-half goal looked to have given Town all three points until Jacob Mellis' 94th minute equaliser.
The Trinidad international, who has been linked with a loan move to former club Swansea recently, slotted in his eighth goal of the season on 82 minutes after Luke Steele had beaten out Lee Martin's strike.
Town were seconds away from chalking up a fourth successive League win until Mellis rescued a point for the home side with virtually the last kick.
Paul Jewell kept with the same side that has served him well over recent weeks, while Danny Haynes lined up for the Tykes, the former Blue forcing a corner in the first foray into Town territory.
Marton Fulop kept out Frank Nouble's shot from the edge of the box before Town lost skipper David Norris with what looked like an ankle injury, Colin Healy his replacement inside the quarter hour.
Jason Shackell had a header dealt comfortably by Fulop from Mellis' free-kick but the 'keeper was made to work a lot harder to deny Garry O'Connor soon after, the Hungary international saving with his feet from the former Birmingham striker after Shackell had won the header.
Town went close to breaking the deadlock on 24 minutes, Jimmy Bullard's free-kick took a heavy deflection and beat Steele, rebounding off the bar. Damien Delaney hooked the ball back into the box and Tamas Priskin headed in but a raised flag from an assistant referee halted Blues' celebrations - the ball judged to have crossed the line for a corner before Delaney made contact.
The Republic of Ireland international was yellow carded for a foul on Haynes as Barnsley broke, Bullard quickly adding his name to referee Darren Drysdale's collection.
Martin fired over from the edge of the box to end a tame first-half on a pitch that made flowing football difficult.
Mellis's free-kick gave Town an early alarm in the second-half , Mark Kennedy eventually clearing the danger, Carlos Edwards then relieved to see his clearance cannon off Haynes and into Fulop's hands.
Nouble's first touch let him down as he raced onto a long ball when clear, then Fulop reacted well to keep out Haynes' deflected left foot strike at the foot of the post.
At the other end it took a great challenge from Shackell to deny Connor Wickham as he got on the end of Grant Leadbitter's pass, Wickham then failing to get any pace of a left foot effort from 15 yards.
Barnsley were forced into their first change just before the hour, the injured Stephen Foster replaced by Kieran Trippier.
Gareth McAuley's header was held by Steele on his line, the 'keeper then denying Martin and Priskin in quick succession as the game sprung into life.
McAuley blocked Haynes' goalbound shot after O'Connor's head down, Steele then keeping out Priskin after Wickham had shown great vision and weight of pass.
Steele was called into action again to prevent Priskin opening the scoring with a drive from 25 yards, Diego Arismendi and then Nouble failing to find the target at the other end.
Blues made a second change on 74 minutes with Scotland on for Priskin, with Barnsley replacing O'Connor with Jacob Butterfield.
Great covering by Healy kept out the danger from Mellis after Haynes' header on, Bobby Hassell heading wide from the resultant corner.
Butterfield exploded a left foot strike that Fulop kept out superbly before Town got the breakthrough, Martin's shot pushed out by Steele and Scotland finding the net from 10 yards eight minutes from time.
Jim O'Brien replaced Arismendi for the last five minutes, Darren O'Dea then on for Bullard.
Martin was booked in added on time after going down in the box, Wickham almost grabbing a second for Town after a surging run into the box but Scotland's goal looked enough to see Blues home until Mellis stuck with virtually the last kick of the game.
Barnsley: Steele, Hassell, Shackell, Foster (Trippier 57), Hill, Mellis, Arismendi (O'Brien 85), Doyle, Nouble, Haynes, O'Connor (Butterfield 75). Subs not used: Preece, Colace, Lovre, Gray.
Town: Fulop, Edwards, McAuley, Delaney, Kennedy, Martin, Norris (Healy 13), Leadbitter, Bullard (O'Dea 86), Wickham, Priskin (Scotland 74). Subs not used: Lee-Barrett, Peters, Smith, Civelli. Booked: Delaney, Bullard, Martin.