The Pole kept his composure to hold off French duo Romain Langasque and Julien Guerrier at Marco Simone Golf & Country Club to win by one shot.
Meronk, who holed the winning putt at the Hero Cup in January, lifted his third DP World Tour title and boosted his hopes of qualifying for the Ryder Cup, which will take place at this course later this year.
Thrilling finale
Meronk and Langasque duelled on the back nine, while overnight leader Guerrier kept in touch with them in a thrilling finale.
The Pole edged ahead on the 16th hole with his fifth birdie of the day and holed a par putt from the edge of the green on the 17th.
Langasque's challenge had appeared to have faltered with a bogey on the 16th, but he stunningly chipped in for a birdie on the penultimate hole to keep the pressure on.
But the Pole would not falter as he birdied the 18th to finish one shot clear of Langasque, with Guerrier a further two back.
Meronk said: "I didn't play as well as previous days so I had to grind a little bit, but I'm proud of myself and my caddie that we kept believing, kept hitting good shots and the putts on 17 and 18 were very big.
"I knew 16 and 18 are birdieable. I had an amazing shot on 16 so that was quite an easy birdie. Seventeen was a bit of a struggle but the putt saved me. On 18 I just focused on making a birdie cos I didn't want to go to a play-off."
Victory on the Ryder Cup course moved Meronk up to fourth in the Race to Dubai Rankings in Partnership with Rolex.
And the 29-year-old is targeting a place in Luke Donald's Europe team for September.
September in sight
Meronk added: "It was definitely on my mind coming here, performing well in front of Luke. I think it might help but there's still a lot of time left. I still have to work on my game and get better to make the team."
Meronk and Langasque started the day on 11 under, a shot adrift of Guerrier. The former immediately picked up a shot on the par-four opening hole for the first time this week before he chipped in from the edge of the second green for a par.
A bogey on the third dropped him back to 11 under, but gains at the fifth and ninth gave him a one-shot lead at the turn.
Langasque, playing in the final pair with compatriot Guerrier behind Meronk, had produced a flawless first eight holes and rounded off the front nine with a birdie.
The pair were tied at the top soon after when the Pole dropped a shot on the tenth despite a stunning chip from the edge of a bunker.
Meronk birdied the 11th to edge ahead again, but Langasque soon matched him.
Meronk had the chance to go to 14 under but narrowly missed his birdie putt on the 12th, with Langasque also parring the hole.
Guerrier, who had three bogeys and a par in his front nine, roared back into contention with a tap-in birdie on the 12th after going close with an eagle effort.
And he was one behind the leading duo after the 13th, with first Meronk and then Langasque both dropping a shot while Guerrier recorded a par.
Langasque's bogey was his first in 34 holes, a run stretching back to Friday, but he soon recorded another on the 14th despite a brilliant attempt at a monster putt for par. Guerrier also dropped a shot to leave Meronk in the lead.
But the Pole's advantage did not last long as he bogeyed the 15th and his French rivals both followed with pars.
It was all set up for a thrilling conclusion as Meronk headed to the 16th tied for the lead with Langasque.
But while Meronk birdied the hole, Langasque found sand off the tee and almost water off his second shot and could not rescue par.
Brilliant putt
Meronk sunk a brilliant putt from the edge of the green on the par-three 17th for par to seemingly give himself a two-shot lead heading to the 18th.
But Langasque was not going away quietly and he brilliantly chipped in from the edge of the green to leave the pressure on.
Langasque, who set a course record on Saturday, finished in style with a birdie, but by then it was not enough to catch Meronk while Guerrier signed for a 73 after finishing with four straight pars.
by DP World Tour