With his cousin, Gunn created 2ge+her for MTV, which started as a television movie and then ran as a series for two seasons. Gunn also was the creator and author of "Redbird Nation," a St. Louis Cardinals fan blog that received high praise during its two years of activity. He co-wrote with his cousin Mark Gunn the screenbook of the Monster Squad remake.

Gunn was born in St. Louis, Missouri. He is one of six children, and the brother of filmmaker James Gunn, actor Sean Gunn, and actor and writer Matt Gunn.