Brigade captain Andy Britton's unbeaten 42 helped his side to a final over win against Carrickfergus to take the Beechgrove side into next week's decider against Cork Harlequins.
Chasing 147, Brigade lost opener David Murdock (11) cheaply, but a second wicket stand of 57 between David Barr (27) and Adam McDaid (38) steadied the ship.
Two wickets for CJ van der Walt (2-23) had the contest in the balance and as the required rate crept towards double figures, the home side were slight favourites despite Brigade having plenty of wickets in hand.
Britton though is the man for the big occasion and he struck three sixes and two fours in his unbeaten 42 from 26 balls, guiding his side to the victory with four balls remaining.
Andy Britton receives the Ulster Cup from Ally McCalmont
He has earlier been the pick of the bowlers, taking 2 for 19 as Carrick posted 146 for 5. One of those was the dangerous Jacques Snyman, and that was the key to the win.
Jeremy Lawlor top scored with 53 from 40 balls (4 fours, 3 sixes), sharing a stand of 88 in 13 overs with CJ van der Walt, who struggled against the spin of Ifty Hussain - his 23 occupying 42 balls.
Graeme McCarter cleared the ropes twice with a few lusty blows late on, but the feeling at halfway was that the target was a little light, and so it proved.
Brigade captain Andy Britton received the Ulster Cup at the end of the game, with the NCU deciding the winners would be presented with the trophy.
The decider at Rathmines will now be played next Sunday, August 22nd, a week earlier than advertised originally, due to Ireland's ODI with Zimbabwe on the 29th.
ALL IRELAND T20 CUP SEMI-FINAL
At Middle Road, Brigade beat Carrickfergus by 6 wickets
Carrickfergus 146/5 (20 overs; J Lawlor 53, G McCarter 23*, CJ van der Walt 23; A Britton 2-19)
Brigade 147/4 (19.2 overs; A Britton 42*, A McDaid 36, D Barr 27; CJ Van der Walt 2-23)