Meronk was the tour player of the year back in 2023 when he was left off the Ryder Cup team in Rome, and then defected to LIV Golf the following year.
He was among eight players who accepted a deal from the European tour earlier this year that's allowed him to keep his membership.
The two-shot victory at St Andrews, his fifth title on the European tour and perhaps the most important, following his final-round of four-under 68 on the Old Course, gives him a full European card for 2027.
That's important with so much in doubt at LIV Golf as it goes through Chapter 11 bankruptcy.
Victory was not secure until Jarvis failed to hole out for eagle from the Valley of Sin on the 18th at the Old Course.
"I never usually cry, but this one feels really special," Meronk said. "I'm lost for words. I'm extremely happy and quite relieved."
He opened with three birdies in five holes to make up a two-shot deficit on Jarvis, the South African going for his third European tour title this year.
Jarvis's chance went when he missed the green well left on the 17th, putted to six feet and missed the par putt.
He closed with a 72 and tied for second with Niklas Norgaard (68), whose amateur partner was outgoing PGA Tour commissioner Jay Monahan.
World No.979 Michael Stewart capped off a dream week with a 66, which included a stretch on the back nine when he made a 25-foot birdie on the 11th, a 30-foot birdie on the 12th and then holed out from 112 yards for eagle on the 13th. He tied for fourth with Tommy Fleetwood (64).
The 20-strong Australian challenge, which had started so brightly when Jack Buchanan led after the first round, ended up fading badly, with only two players making the third-round individual cut - Declan O'Donovan, who finished joint-55th on six-under after a 73, and Cameron John (tied-61st at six-under after a 74).
