John Colapinto (born in 1958) is a Canadian journalist, author and novelist and a staff writer at The New Yorker. In 2000, he wrote the New York Times bestseller As Nature Made Him: The Boy Who Was Raised as a Girl, which exposed the details of the David Reimer case, a boy who had undergone a sex change in infancy—a medical experiment long heralded as a success, but which was, in fact, a failure.

Before working on staff at The New Yorker, Colapinto's articles appeared in Vanity Fair, Esquire, Mademoiselle, Us, New York and The New York Times Magazine, and in 1995 he became a contributing editor at Rolling Stone.

He also wrote the screenplay for the 1990 Canadian short film The Star Turn.

For Rolling Stone, Colapinto wrote feature stories on a variety of subjects including AIDS, kids and guns, heroin in the music business, and Penthouse magazine creator, Bob Guccione.

In 1998, Colapinto published a 20,000 word feature story in Rolling Stone titled "The True Story of John/Joan", an account of David Reimer, who had undergone a sex change in infancy following a botched circumcision in which he lost his penis. The medical experiment had been long heralded as a success, but was, in fact, a failure. The story, which detailed not only Reimer's tortured life, but the medical scandal surrounding its cover-up, won the ASME Award for reporting. In 2000, Colapinto published a book-length account of the case, As Nature Made Him: The Boy Who Was Raised as a Girl. The book was a New York Times bestseller and the film rights were bought by director Peter Jackson. Reimer took his life in 2004.

Colapinto also wrote a novel, About the Author, a tale of literary envy and theft. It was published in August 2001 and was a number six pick on the Book Sense 76 list of best novels of the season; it was a nominee for the International Dublin Literary Award and for a number of years was under option by DreamWorks where playwright Patrick Marber wrote a screen adaptation. The film rights to the novel were acquired by producer Scott Rudin but a shootable screenplay failed to materialize and Rudin allowed his option to lapse. In the spring of 2023, the novel was optioned by Tr-Star Pictures and is, as of 2024, in development at that studio.

Colapinto's second novel, Undone, a satire hingeing on faux-incest, was published by HarperCollins Canada in April 2015. It was rejected by 41 US publishers and every publisher in Europe on grounds that it was too challenging in its subject matter. A newspaper feature story in The Globe and Mail gave an account of the novel's universal rejection in Colapinto's adopted country. A highly positive review in the Toronto Star called Undone "an equally inventive but bolder novel" than Colapinto's debut; a review in the Globe and Mail called the novel "a noir that, like Francine Prose's Blue Angel and Philip Roth's American Pastoral, details the unravelling of the moral American man and his world."

In June 2015, Colapinto spoke about the novel, and its difficult publishing history, on the CBC Radio program "q":