Marrar ended East Wagga-Kooringal's unbeaten season to secure back-to-back premierships in the under 17.5s.
The Hawks had dominated all season, including a 52-point win in the second semi-final, but couldn't sustain their run at Robertson Oval on Saturday.
It was tight throughout the first three quarters before the Bombers continued to lift.
Taking a two-point lead into the final change they kicked the first three goals of the quarter to set up the victory.
Coach Paul Jenkins was thrilled with the 11.13 79 to 8.15 63 win.
"We knew that if we could make it through to the end of the year you never know what might happen and we were lucky to get away with the win," Jenkins said.
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The closest the Bombers had been to the Hawks was the previous finals game.
However buoyed by the return of Adam Whyte, Toby Lawler and Drew Beavan, who was named best on ground, from first grade and others back from injury, Jenkins thought the boost in number helped counter the minor premiers.
"We only had one on the bench that day and it makes a huge difference," he said.
Beavan's class proved valuable late in the game while Lawler created and then finished their first goal of the last quarter.
A minute later the Bombers had another as Jamie Mooney slotted his fourth for the game before Abdallah Farah sealed the win with his second.
Jeremy Piercy kicked a late goal for the Hawks but they didn't have enough answers after being on top for large periods of the first half.
The two sides went goal-for-goal in the first quarter before the Hawks extended their advantage to 15 points early in the second quarter through Cayleb Dunne-Argus.
However the Bombers were able to turn the tide with goals to Sam Emery, Mooney and Lawler giving the Bombers a five-point lead at the main break.
Marrar went out to a two-goal lead eight minutes into the third quarter through goals to Farrah and Mooney before the momentum swung back.
The Hawks edged themselves back in front with the next three goals before a lovely finish from Beavan handed Marrar back the lead and they never let it go.
Marrar 2.4 5.7 8.10 11.13 (79)
EWK 3.4 4.8 7.14 8.15 (63)
Goals: (Marrar) J Mooney 4, S Emery 2, T Lawler 2, A Farah 2, D Beavan 1; (EWK) K McMahon 2, J Piercy 2, C Dunne-Argus 2, M Aitken 1, T Piercy 1.
Best: (Marrar) D Beavan, T Lawler, A Howard, N Cawley, S Emery, B Walker; (EWK) H Mitter, K Wilson, J Piercy, Z Randall, T Piercy, P Naumann.
Best on Ground: Drew Beavan