Justin Monjo is the son of American writer F. N. Monjo, who wrote over twenty children's books. Justin Monjo was born in New York City, and came to Australia in the mid-1980s to study acting at the National Institute of Dramatic Art. He worked as an actor for ten years before switching to writing.
Monjo's earliest television scripts were for police drama Wildside (1997-1999). He followed this with the script for American feature film Cement (2000), the neo-noir crime film that marked American actor Adrian Pasdar's directorial debut: the film won awards at both the AngelCiti Film Festival and WorldFest Houston. Monjo followed Cement with scripts for another Australian crime drama, 2002's Young Lions.
Monjo's largest body of work during the late 1990s and early 2000s, however, was for American-Australian science-fiction program Farscape. Of the nine Australian script-writers who worked on Farscape, Monjo was the single most prolific, scripting fourteen of the program's eighty-eight episodes, earning a 'creative consultant' credit on a number of others, and working as co-executive producer for the program.
Monjo continued to produce individual scripts for television programs after the cancellation of Farscape in 2003, including for The Strip and Rush. In 2004, he scripted the successful tele-movie The Alice, which led in 2005 to the spin-off television series The Alice, co-created by Monjo and Robyn Sinclair, but cancelled after a single season. Since then, his work has included the Russell Mulcahy shark-attack film Bait (2012) and the forthcoming Paper Giants: Magazine Wars and Three Dog Night (both slated for 2013).
Monjo's theatrical work includes Romeo Is Bleeding, That Eye, The Sky, and Cloudstreet (co-written with Nick Enright).