On a night of unparalleled drama at the Nou Camp, Terry looked to have pressed the self-destruct button on the Blues' hopes of glory on the continent when he saw red for kneeing Alexis Sanchez from behind.
But the 10 men were simply magnificent for the rest of the second leg, fighting back from goals from Sergio Busquets and Andres Iniesta with a stunning chip from Ramires before half-time.
And after surviving a Barca siege from start to finish that saw Lionel Messi miss a penalty, Fernando Torres came off the bench to score a stoppage-time breakaway goal as Chelsea avenged their 2009 defeat in the most dramatic manner possible with a 3-2 aggregate victory.
Reaching their second final came at a huge cost, with Terry's red card and yellows for Ramires, Branislav Ivanovic and Raul Meireles ruling them out of the final.
But they will worry about that in the morning after celebrating arguably the greatest result in the club's history and one which may finally convince Roman Abramovich to make Roberto Di Matteo's appointment as manager permanent.
Disaster struck for Chelsea as early as the sixth minute, Gary Cahill eventually forced off after slipping and pulling his hamstring, with Jose Bosingwa coming on and Ivanovic forced to move to centre-back.
It was soon 1-1 on the injury front, Gerard Pique lasting just 26 minutes of his recall after failing to recover from a sickening collision with the backside of Victor Valdes that appeared to leave him briefly unconscious.
That failed to alter the pattern of a game which was a carbon copy of the first leg as Chelsea parked the bus once more.
Messi rippled the side-netting inside three minutes and, after both sides' injury woes, he should have opening the scoring in the 20th minute, firing a one-two with Cesc Fabregas against Petr Cech's leg.
Fabregas also volleyed into the sidenetting and Cech tipped over Javier Mascherano's drive but there was hope for Chelsea before Pique's departure when Didier Drogba shrugged him off but could himself only find the side-netting from the tightest of angles.
The first sign of Chelsea's discipline wavering came when John Obi Mikel was booked for chopping down Alexis Sanchez in the 32nd minute.
And when they went to sleep three minutes later, they were behind, their failure to close down allowing Isaac Cuenca to square for Busquets to tap into a virtually unguarded net.
The build-up to this tie was dominated by talk of refereeing meltdowns in previous clashes but Terry simply gave Cuneyt Cakir no choice but to dismiss him less than two minutes later.
Sanchez over-reacted to the swipe, bringing back memories of David Beckham's 1998 World Cup sending-off, and Terry initially refused to walk.
But Cech made him listen to reason before picking the ball out of his own net again two minutes before half time, Chelsea carved apart as Messi teed up Iniesta to stroke the ball home.
Chelsea looked dead and buried but, as at Stamford Bridge, they struck a dagger blow with their first shot on target in first-half stoppage-time.
Frank Lampard was again the creator as Ramires burst through and floated a glorious finish over Valdes - moments after picking up a booking that would rule him out of the final.
The cascade of noise that had filled the Nou Camp turned to silence at half-time but they were soon cheering again after the restart when Drogba conceded a penalty.
Cakir adjudged the striker had tripped Fabregas and pointed to the spot, with Ivanovic cautioned for his protest.
It looked certain Messi would end his Chelsea hoodoo but, incredibly, he smashed his effort against the crossbar.
Lampard was fortunate to escape punishment for a flare-up with Fabregas, Sanchez nodded substitute Daniel Alves' cross wide, and Cech was booked for timewasting having already been warned before saving well again from Cuenca.
Ivanovic almost capitalised after Drogba helped Chelsea win a rare corner but he was warned himself after going down theatrically, while Lampard was lucky to only see yellow for cutting down Fabregas after Messi was booked for tugging him back.
The visitors were hanging on and were given two lifelines in 60 seconds in the final 10 minutes when Sanchez had a goal ruled out for offside and Messi hit the post from 20 yards.
With time running out, Meireles was ruled out of the final after being booked for fouling Mascherano, who Cech saved from again in the final minute.
And then, in stoppage-time, a long clearance found substitute Torres with 50 yards of space in which to run.
Unlike most of his Chelsea career, he made no mistake, rounding Valdes and slotting home to jubilant scenes.