Nardiello, who was substituted after a poor performance against Huddersfield in the first leg, gleefully slammed in the rebound after Paul Rachubka spilled Brian Howard's long-range blockbuster on 77 minutes.
Barnsley looked beaten when Town skipper Jonathan Worthington carried the tie into Huddersfield's advantage by tapping in from close range after striker David Graham beat Tykes keeper Nick Colgan to Stephen McPhail's weak backpass.
It made the score 2-1 to Huddersfield on aggregate after Barnsley had got back into the contest through Paul Hayes' penalty.
But the visitors found incredible reserves of character to hit back and they were level on aggregate on 71 minutes when Paul Reid headed in unmarked from Martin Devaney's corner, after Bobby Hassell's flick-on took out the entire Town defence.
Shell shocked Town were hardly in it after that but could have taken the contest into extra time with nearly the last kick of the game, but Gary Taylor-Fletcher blasted wide after Andy Booth flicked on a Danny Schofield cross.
Barnsley looked dangerous on the break in the first half and were only prevented from taking the lead on 44 minutes when Booth cleared Howard's goalbound effort off the line, after Rachubka failed to deal with Devaney's cross.
Howard also wasted a great chance to score on 43 minutes when his break from midfield went unchecked and the goal seemed to open up in front of him.
Howard should have had a pop at the target, but instead misplaced an attempted pass wide for the oncoming Nardiello.
Huddersfield started well and kept the visitors pressed inside their own half in the early stages but could not find a way through.
Booth came closest with an angled volley that flashed just wide of the bar on seven minutes from Schofield's curling delivery.