At the age of eleven, Callahan toured with a children's musical group through thirty-seven states. At fifteen he received his first acting role in the television series The Wonder Years. After honing his acting skills in television he tried for the big screen and soon appeared in various films. Inspired by the Directors he worked with Callahan decided to try working behind the camera and in 1998 shot his first short film The Red Bag.
In a 2007 interview with The Hollywood Reporter, Callahan revealed that he has had serious health problems when doctors found a tumor in his right kidney. He lost his right kidney and right adrenal gland, and has been in and out of a wheelchair for years.
Callahan cashed in 94th place in the 2011 World Series of Poker main event, earning $64,531.
