Rene Charlebois, 48, was discovered missing Saturday night during a headcount by staff at a minimum-security prison in Laval.
The 48-year-old was convicted on murder charges during the 2003 megatrial against the Hells Angels biker gang.
He is also doing time for drug-related convictions.
Quebec provincial police are asking for assistance to help track him down.
Charlebois is five feet eight inches tall with brown eyes and brown hair and has his first name tattooed on his left arm.