The Pole entered the day at Victoria Golf Club a shot behind former World Number One Adam Scott but after a two-shot swing on the first he never looked back, signing for a 66 to finish at 14 under.
Scott carded a 72 in front of adoring home crowds to finish a shot ahead of another Australian in Min Woo Lee, who recorded a closing 69.
Spaniard Alejandro Cañizares signed for a 64 to finish at seven under alongside Australia's Haydn Barron, one clear of Kiwi Josh Geary.
Lee, Cañizares and Barron all booked their places at The 151st Open Championship at Royal Liverpool thanks to their finishes.
In the women's event, South Africa's Ashleigh Buhai finished a shot ahead of South Korean Jiyai Shin, while Kipp Popert cruised to victory in the G4D Tour season opener, winning the Australian All Abilities Championship @ the ISPS HANDA Australian Open by seven shots.
Meronk made the trip Down Under after a 2022 season that saw him become the first Polish player to win a DP World Tour event thanks to his triumph at the Horizon Irish Open and finish eighth in the Rankings.
He was four over after his first 16 holes in Melbourne and looked like he could be in a battle to make the cut after a 73 but followed that up with rounds of 66-63-66 to storm to the top of the leaderboard and take the trophy.
“I’m super excited and to finish like that on the 18th hole is just unreal," he said. “I’m so grateful, thank you for all the support and I enjoyed this week so much.
“I felt really good again today. I kept doing what I’ve done the last two days and it worked pretty well. I’m super proud of myself, proud of my team and super happy right now."
There was a two-shot swing on the first as Scott dropped a shot and Meronk made a birdie and the lead was two when the 29-year-old put an approach to four feet on the next.
Scott came roaring back as he holed a 15-footer on the fourth and put an approach to two feet on the fifth but he bogeyed the seventh to once again drop out of the lead.
He failed to get up and down from the sand on the eighth and with Meronk making a two-putt birdie on the par-five ninth, the Pole led by three at the turn.
Scott hit a smart approach into the 12th to trim the lead and made a good par save at the next, with Meronk unable to do the same from the greenside bunker.
A wonderful bunker shot on the driveable 15th helped set up a birdie and while Meronk gave that shot back on the 17th, Scott went out of bounds off the tee to surrender a double-bogey.
That gave Meronk a three-shot cushion heading up the last and he completed an emphatic victory by holing a long putt from just off the 18th green to spark wild celebrations.
Lee started his day with an eagle from 20 feet at the first but never gained enough momentum to seriously challenge as he birdied the ninth and 15th but dropped shots on the eighth, tenth and 16th.
His third-place finish is his third in his last six events, with a worst result of 12th, as he rediscovers the form that made him a Rolex Series winner.
Barron got one of the biggest cheers of the day as he eagled the last in a 70, a score matched by Geary.
Australians Andrew Martin and Matthew Millar and Irishman Conor Purcell finished at five under, a shot clear of a group of seven players including Lucas Herbert, Nicolai Højgaard and Tom Lewis.