Town were 30 minutes from the Carling Cup Final until goals from Nicklas Bendtner, Laurent Koscielny and Cesc Fabregas sent Arsenal to Wembley.
Bendtner sent a superb curler past Marton Fulop on 61 minutes and then Koscielny put the Londoners ahead over the two legs with a header from Andrey Arshavin's corner three minutes later.
Jason Scotland forced Wojciech Szczesny into a save as Town looked to get back in the game but Fabregas secured Arsene Wenger's side a date with either Birmingham or West Ham with a left foot finish 13 minutes from time.
Town made one change to the side that beat Doncaster at the weekend, Mark Kennedy coming back in for the cup-tied Lee Martin.
Grant Leadbitter had an audacious first attempt at goal from the kick-off, the ball landing on the roof of the net. Robin Van Persie almost threaded a ball through the Town defence a minute later, the Dutchman then volleying wide from 10 yards following Bacary Sagna's cross.
Fabregas went down looking for a penalty on 11 minutes but Gareth McAuley made minimal contact and referee Mark Halsey was rightly not interested in the Gunners' appeals.
McAuley sent a header over from a Leadbitter free-kick on the quarter-hour in Blues' best effort at goal in the first 45 minutes. Sagna was then forced off after taking a blow to the head from goalkeeper Szczesny as they both challenged Town's Northern Ireland international.
Emmanuel Eboue replaced the clearly shaken up Sagna but Town refused to be shaken up by the Gunners' attacks, Fulop saving well from Fabregas.
Van Persie sent a header against the bar from Bendtner's cross before Connor Wickham picked up the first yellow card of the game for a foul.
Damien Delaney continued where he left off in the first-leg, throwing himself in the way of Bendtner's effort after Fulop couldn't clear the danger from a Fabregas free-kick.
Fulop denied Fabregas although the offside flag had already come to Town's rescue, Koscielny yellow carded for a foul on David Norris.
Fabregas dragged a great chance wide after a sublime touch to control a terrific pass from Jack Wilshere, with Darren O'Dea bringing the half to an end with more resolute defending to deny Van Persie.
O'Dea was immediately in the action after the restart, at the other end this time, volleying wide after Arsenal failed to deal with a Leadbitter corner.
Fabregas failed to connect 10 yards out as Arsene Wenger's side looked to break the Blue line, Kennedy in the right place again to clear from Van Persie.
Delaney put behind Wilshere's dangerous cross but the opener came on the hour, Bendtner taking Wilshere's long range pass inside Carlos Edwards and curling the ball superbly past Fulop from the edge of the box.
Town made a first change with Priskin making way for Scotland but the striker hadn't touched the ball before Arsenal went ahead in the tie, Koscielny heading in from a corner.
Scotland forced a save from Szczesny after Colin Healy's clever pass, Norris then thwarted as he tried to feed Wickham inside the Arsenal box.
Shane O'Connor replaced Healy for the last 15 minutes in Town's second change, Fabregas dragging a shot wide after weaving inside the Blues' box.
It was the Spanish midfielder who clinched the Gunners a place at Wembley on 77 minutes though, burying a left foot shot past Fulop from 10 yards out to end Town's Carling Cup campaign one step from Wembley and leave Arsenal 3-1 winners on aggregate..
Arsenal: Szczesny, Sagna (Eboue 18), Koscielny, Djourou, Clichy, Wilshere, Denilson, Fabregas, Arshavin (Walcott 84), Bendtner, Van Persie (Nasri 84). Subs not used: Song, Gibbs, Chamakh, Shea. Booked: Koscielny.
Town: Fulop, Edwards, McAuley, Delaney, O'Dea, Norris, Kennedy, Healy (O'Connor 75), Leadbitter, Wickham, Priskin (Scotland 62). Subs not used: Peters, Lee-Barrett, Hyam, Smith, Civelli. Booked: Wickham.