William Shunn was born in Los Angeles and raised in Utah, the eldest of eight children in a devout Mormon family. A writer from a young age, he attended the Clarion Writers Workshop at Michigan State University in 1985, when he was 17. As was expected, he departed on a proselytizing mission for the LDS Church at the age of 19. He was assigned to preach in Alberta, Canada, but after six months he was convicted of felony mischief in connection with a false bomb threat and expelled from the country. The complete story is recounted in his memoir The Accidental Terrorist, available November 10, 2015.

A small collection of his stories, An Alternate History of the 21st Century, was published by Spilt Milk Press in 2007, with an introduction by Cory Doctorow. Cast a Cold Eye, a short horror novel co-written with Derryl Murphy, appeared from PS Publishing in 2009.
Shunn served three years as a national juror for the Scholastic Art & Writing Awards, and for three years hosted and produced the acclaimed Tuesday Funk literary reading series in Chicago. He has long worked as a software developer, notably for WordPerfect Corporation and Sesame Workshop, and on September 11, 2001, he created what may have been the first online "survivor registry," a database that allowed people in affected cities a way to report their status and allowed friends and families to see if their loved ones were okay.
William Shunn left the Mormon Church in 1995 and developed one of the earliest ex-Mormon web sites. He lives in New York City.