He finished three shots ahead of 18-year-old Duncan Croudis (Otago), who had won the three previous trial events to make a bid for the top slot.
Some awkward pin placements and gusty winds prevented the top players from scoring low, with McEwan finishing 1-over-par for the four rounds.
Croudis took the early lead with a 1-under 71 on Saturday morning, with McEwan and Cody Harper (Invercargill) one shot back.
McEwan went under the card in the afternoon to lead at the halfway stage, with Croudis, Harper and Tyrone Ratahi (Otago) tied for second two shots back.
The trio held a five-shot advantage over the rest of the field and the tournament looked set to be a four-player race.
McEwan was the epitome of consistency, following his 72 and 71 with another 72 on Sunday morning.
Croudis shot a 73 to be three shots back while Ratahi and Harper both fired 74 to be a further stroke behind.
Liam Balneaves (Greenacres) was the mover yesterday morning, with a 69 for the lowest score of the weekend to get up for a tie for third.
In the final round, Harper shot 76, Ratahi a 77 and Balneaves a 78 leaving McEwan and Croudis to battle for the title.
Despite a three-shot swing to Croudis on the par -5 hole, both shot 74 in the final round to give McEwan the title.
