The ten-year vegan competed in the 32nd annual Nautica Malibu Triathlon in Los Angeles and placed tenth in the celebrity division.
In a celebratory Instagram post, he said that there were 'tons of celebrities' at the event, so he was 'stoked' about his results.
'Healthy as f***'
Steve-O has been working on his fitness for months.
In June, he took to Instagram and wrote: "For my birthday this year, I decided to get in the best shape I've ever been in. I may be old, but I’m healthy as f***!"
He later shared a post which included a picture of himself and his partner after a run, to announce the upcoming event.
Despite the conclusion of Jackass in 2002, Steve-O - whose real name is Stephen Glover - continues to perform over-the-top stunts.
He's also known to use his showmanship for activism.
In 2015, the star was jailed for climbing a 100-foot crane on Sunshine Boulevard in an anti-SeaWorld demonstration.