The 23-year-old set up the win with a remarkable eagle at the par-5 15th at Nudgee GC on Sunday where he rifled a 6-iron from a muddy lie to 12 feet before draining the putt to draw level with overnight leader Zach Murray.
John backed that up with a birdie on the 16th - a hole that Murray bogeyed - and then made clutch pars on 17 and 18.
He signed for a six-under 66 and a four-round total of 17-under 271, two shots clear of teenaged amateur sensation Billy Dowling, who shot 64-66 on the weekend.
Murray (70) finished outright third, a shot behind Dowling.
John was already assured of starts in next week's Australian PGA at Royal Queensland and the December 4-7 Australian Open at Royal Melbourne.
But buoyed by his 15th hole heroics on Sunday, he will enter the two DP World Tour co-sanctioned events with his confidence sky-high.
"I had 220 (metres) to the flag and I knew I was pretty amped," said John, who trailed Murray by two at the time.
"There was a lot of washed clippings and stuff that had sort of gathered up there. It was a bit of a run-off. I asked for a ruling and the clippings were loose impediments so I could get some sort of lie in there.
"It's still in mud and still dirt and it was just one of those ones where you're so amped and just got to flush it and keep moving on.
"I was like, if I'm going to win this tournament, I've got to hit this shot. And fortunately for me, I obviously was able to pull it off."
It was John's second win on the Australasian Tour, having also saluted at The National Tournament in 2024.
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