Goals either side of the half time break helped the eventual winners, who led by double scores at the interval.
The sides were evenly matched for a large part of the opening period before a Jason Murphy three-pointer pushed Mullaghbawn further in front. 1-7 to 0-5 at half time.
Killeavy pushed on in the second half and four points in the trot dwindled the deficit down to just one.
Mullaghbawn had the final say however and a goal near the end of the game from Aaron Tavey ensured their passage to the showpiece.
They will now take on Crossmaglen in the under 19 final, with the date time and venue all to be confirmed.
In Division Two, the final pairings were also decided at the weekend, and it’ll be Culloville taking on Silverbridge.
The Blues overcame Pearse Og in their last four battle, with nine-points the difference in the end.
Culloville led by four points at the half time break, with the scoreboard reading Culloville 0-7 Pearse Og 0-3.
Five goals followed in the second half, with Culloville hitting three of them to get them over the line.
Charlie Garvey was responsible for two of those three-points while Ciaran Connolly also hit the back of the net.
Starman Dara Quinn finished with 0-5 of their final tally while Ryan Duffy (0-2), Fergal Kieran (0-2) and Taidgh O’Neill (0-1) all chipped in with scores.
The Ogs claimed two goals after the turnaround, but Culloville were too good on the day and ran out 3-11 to 2-5 winners.
Silverbridge overcame a much sterner test from Carrickcruppen and just one point separated them in the end.
The Harps just about got over the line to secure their place in the decider, winning 0-10 to 0-9 in the end.