A 1983 graduate of Princeton University, he has published a collection of short stories and several novels, including Thumbsucker, which was made into a 2005 film featuring Keanu Reeves and Vince Vaughn; Up in the Air, a feature film directed by Jason Reitman; and Mission to America. In 2005, he took over pioneer blogger Andrew Sullivan's shoes for a few weeks while Sullivan was on vacation. He has also written The Unbinding, an Internet-only novel that was posted in Slate magazine.

He has also reviewed books for New York Magazine and has written for The New York Times Book Review and New York Times Sunday Magazine, and is a contributing editor of Time, where he has received popularity for his entertaining and sometimes humorous first-person essays among other articles of interest. He also served as an American cultural correspondent for the BBC.

In addition to teaching nonfiction writing at the University of Montana, Kirn was the 2008-09 Vare Nonfiction Writer in Residence at the University of Chicago. He received his B.A. English at Princeton University in 1983, and studied English Literature at Oxford University.

Kirn's family joined The Church of Jesus Christ of Latter-day Saints when he was twelve, but Kirn is no longer affiliated with the church. NPR: Writer Walter Kirn, on a 'Mission to America' Kirn received the 2009 William Law X-Mormon of the Year award. Kirn married Maggie McGuane, a model and the daughter of actress Margot Kidder and novelist Thomas McGuane, in 1995. Kirn was 32 at the time; McGuane was 19. The couple had two children, Masie and Charlie, and are now divorced.