The Cobblers gave a superb performance in the second leg at Whaddon Road against Cheltenham Town and confirmed their Wembley place through a superb 25 yard strike from Luke Guttridge on 28 minutes, which gave them a 1-0 victory (2-0 on aggregate).
10 minutes before that goal Lee Nicholls brilliantly saved Marlon Packs' penalty, earning plenty of praise from boss Aidy Boothroyd after the game.
"Lee Nicholls was outstanding," he said.
"I was very fortunate to work with Ben Foster and I genuinely think Lee is as good as he is."
Cobblers opponents will be Bradford City who came from behind to beat Burton Albion 3-1 after losing the home leg 3-2.