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Having initially retired in 2013, the Canadian returned to the Octagon in November 2017 to beat Michael Bisping for the middleweight title, becoming the fourth multiple-weight champion in the sport's history
In total he won 26 of his 28 fights and he believes the time has come to bow out.
"In combat sport that's how you should retire - on top," said St-Pierre. "The career of an athlete is not a straight line and it's important right now and to this day that I remember the positives of everything.
"When I was young, the reason that I started mixed martial arts is that I watched Royce Gracie growing up when he won the first UFC and at that particular moment I knew exactly that's what I wanted to do.
"It's like I had a vision and I want to thank Royce Gracie to have inspired me.
"There's no tears, I'm very happy to do it. It takes a lot of discipline though to retire on top.
"It was a long process in my mind but it's time to do it. Only a few people have done it and I always said I wanted to retire on my own and not be told to retire."
Getty Images/Mike Stobe