At UFC 69, St-Pierre lost the welterweight title to The Ultimate Fighter 4 winner Matt Serra when Serra forced the referee to step in after a series of unanswered strikes at of round one.
As a child he played hockey, skated and participated in several sports.
He began learning Kyokushin karate at age seven from his father and later from a Kyokushin Karate Master to defend himself against a school bully.
St-Pierre began training with Rashad Evans, Nathan Marquardt, Keith Jardine, Donald Cerrone and other mixed martial arts fighters at Greg Jackson's Submission Fighting Gaidojutsu school in New Mexico.
Some of Jackson's students accompanied St-Pierre to Montreal to help prepare him for his fight at UFC 94 against B. Penn at the Tristar Gym, including Keith Jardine, Nathan Marquardt, Donald Cerrone and Rashad Evans.
St-Pierre controlled the fight and eventually sneaked in a rear naked choke with less than a minute remaining in the first round. St-Pierre won the match by split decision and was set for a rematch against then-champion Matt Hughes at UFC 63. The UFC announced afterward that St-Pierre would have the opportunity to fight for the title when his condition was fully healed.