McGregor last fought earlier this year and beat Donald 'Cowboy' Cerrone in just 40 seconds in Las Vegas.
He took to Twitter earlier this morning to announce the news alongside a picture of his mother.
The post says - "Hey guys I’ve decided to retire from fighting. Thank you all for the amazing memories! What a ride it’s been!"
"Here is a picture of myself and my mother in Las Vegas post one of my World title wins! Pick the home of your dreams Mags I love you! Whatever you desire it’s yours 
"
