The Doctor Who star, 57, was part of the sixth series of the Channel 4 reality show, which returned to TV screens on Sunday evening.
The first episode showed celebrities taking part in SAS winter warfare training in the south islands of New Zealand.
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Barrowman, who opened up about the flashing allegations he faced in 2021 while on the show, could be seen throwing up sometime after the first challenge.
After the contestants put on their uniforms and got ready to see their accommodation, Barrowman vomits and tells the group “I’m out”.
Asked by Mark “Billy” Billingham if he would like to see a doctor, Barrowman then said: “No… I’m done.”
He added: “I just… it’s not for me, I know who I am and what I’m about, it’s not for me.”
The programme’s narrator said: “After only 32 minutes on base, number 13 John is the first recruit to leave the course.”
During the episode, Barrowman addressed the accusations that he had repeatedly exposed himself on the set of the BBC One sci-fi series Doctor Who and its sister show Torchwood.
He said: “The press made the allegation that I was going around putting my d*** on everybody’s shoulders.
“Having that happen to me ruined me, but this course is going to help me push through this and I want people to see the kind of person that I really am.”
He later added: “On Doctor Who and Torchwood, I had to do a lot of nude scenes. If I were being stupid, I would do something stupid.
“I would shake and waggle or I might do a scene where I might have one of my b******* hanging out.
“The press made it out that I was a sexual deviant. We’ve all done stupid things and silly things, but what’s been said about me will never go away now.
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Contestants in this series include Rachel Johnson, who is the sister of former prime minister Boris Johnson, reality star Pete Wicks, former Olympic gymnast Ellie Downie, comedian Tez Ilyas, professional basketball player and Love Island star Ovie Soko and world heavyweight champion boxer Lani Daniels.
Reality TV Star Bianca Gascoigne, former England rugby captain Chris Robshaw, TV Presenter Cherry Healey, former professional boxer Anthony Ogogo, comedian Shazia Mirza, Love Island contestant Georgia Harrison, reality star Bobby Norris and former Geordie Shore star Marnie Simpson complete the line-up.
Series six of Celebrity SAS: Who Dares Wins will air on Channel 4 every Sunday and Monday from September 22, at 9pm.