Pat O'Brien is a guitarist for the death metal band Cannibal Corpse and live guitarist for black metal band Trelldom. He currently resides in Florida. He has writing credits on some of Cannibal Corpse's more complicated songs, including "Hatchet to the Head," "Systematic Elimination," "Frantic Disembowelment" and "Blunt Force Castration." He is featured on the albums Gallery of Suicide, Bloodthirst, Gore Obsessed, Worm Infested, The Wretched Spawn, Kill, and Evisceration Plague.
He also played in death/thrash metal band Ceremony for a while.
He also played guitar for Nevermore from 1994 to 1996.
Pat O'Brien joined Cannibal Corpse in 1997 after recording The Politics of Ecstasy with Nevermore in 1996, replacing Rob Barrett on guitars.