McGregor, who helped bring MMA to a mainstream auidence like no other fighter in recent times, made his announcement on Twitter on Tuesday morning.
"Hey guys quick announcement, I've decided to retire from the sport formally known as "Mixed Martial Art" today," he wrote.
"I wish all my old colleagues well going forward in competition.
"I now join my former partners on this venture, already in retirement.
"Proper Pina Coladas on me fellas!"
The 30-year-old retires with a record of 21-4.
McGregor instantly shot to stardom in UFC, winning performance of the night three times in succession after defeating Diego Brandao, Dustin Poirier and Chad Mendes.
In December 2014 at UFC 194, he recorded one of the biggest knockout wins in the promotion's history, flooring Jose Aldo inside 13 seconds.
The Dubliner then shared a blitstering rivalry with Nate Diaz, losing his first fight in UFC to the American at UFC 196 before winning a rematch five months later.
Still featherweight champion, McGregor added lightweight gold to his collection when he comfortably beat Eddie Alavrez at UFC 205.
After stepping away from MMA, McGregor took on Floyd Mayweather in what was his first professional boxing match, losing by TKO in the 10th round.
The Irishman wad forced to vacate his featherweight title but returned to UFC to defend his lightweight strap against Khabib Nurmagomedov on an explosive card in Las Vegas last October.
McGregor tapped out for the second time in his UFC career with a mass brawl taking place inside and outside the octagon in the aftermath, with both fighters receiving hefty fines.
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