The Bees took full advantage of a woeful first-half performance from Exeter at St James Park to claim a 3-2 aggregate triumph and book a Wembley appearance for the first time since 1995.
Myles Weston provided the assist for both goals with his first cross finding Sam Saunders at the back post, who rammed the ball into the roof of the net in the 20th minute.
Jusdt six minutes later Weston got the better of Richard Duffy before delivering a fine cross that Gary Alexander headed emphatically past former Bees loanee Ben Hamer to make it 2-0 and 3-1 on aggregate.
Brentford were better all over the park and had plenty of opportunities to extend their lead.
Exeter were poor and rarely threatened the home goal, with Daniel Nardiello their only true threat. And it was Nardiello that gave Exeter a small glimmer of hope when he curled a fine shot into the bottom corner deep into stoppage time, but it was too little too late from the Devon side.