Villa battled back to cancel out a couple of goals by Nikola Kalinic to set Villa Park alight with a ten-goal thriller.
Blackburn gave Villa a major scare and the vital turning point occurred when Christopher Samba was sent off in the 39th minute to enable James Milner to level the scores from the penalty spot.
Stephen Warnock had earlier pulled back a goal and the other four scorers for Villa were Stephen N'Zonzi (own goal), Gabriel Agbonlahor, Emile Heskey and Ashley Young.
But Blackburn battled right until the end with a couple of late goals from Martin Olsson and Brett Emerton to leave Villa's nerves jangling on a knife-edge.
Manager Martin O'Neill, who has described his current side as Villa's best team in over a decade, was obviously delighted.
He is no stranger to League Cup success as he was twice in the Nottingham Forest side which won the trophy and also twice guided Leicester City to success.
With a one-goal advantage from the first leg, Villa badly needed to build on their slender lead but Blackburn were by far the more positive as they strived to get back on level terms.
They began where they left off in the first leg and their persistence was rewarded in the tenth minute. Goalkeeper Brad Guzan flapped at David Dunn's corner and Kalinic was on hand to head home off the back of Warnock.
It was hardly the kind of event the fervent Villa fans had expected and it certainly put the home side off their stride.
In contrast a boosted Blackburn team continued to pressurise Villa and the home team's defence was unusually jittery.
It was therefore no surprise when Blackburn stormed further ahead in the 26th minute. Morten Gamst Pedersen had loads of space on the left and his cross was headed goalwards by Olsson only for Guzan to parry the effort into the path of Kalinic to notch his second goal.
But the game went back into the boiling pot when Villa restored some pride in their performance.
Young's cross from the right found the unmarked Warnock who lashed his shot into the roof of the net for his first goal of the season.
The all-action thriller reached fever pitch in the 39th minute when Samba was sent off after bringing down Agbonlahor.
Referee Martin Atkinson had no hesitation in sending off the Rovers defender and awarding a penalty which Milner hammered into the net.
The decision completely changed the course of the game which was then dominated by Villa before Blackburn staged a mini-revival.
Eight minutes into the second period Richard Dunne was on hand to push a corner goalwards and it was turned into the goal by N'Zonzi.
Villa's flag-waving fans were then assured of a trip to Wembley when Milner's shot was chested home by Agbonlahor in the 57th minute.
In this high-scoring game, Heskey got onto the goal sheet after collecting a 63rd minute pass from Milner.
The eighth goal of this Cup thriller came from Olsson with an excellent snap-shot which easily beat Guzan in the 65th minute.
Emerton then converted Pedersen's 84th-minute corner but Young put the issue beyond doubt with an 90th-minute goal that extended Villa's unbeaten home run against Blackburn to seven games.