Mr. O'Brien has twice won the prestigious Silver Logie Award (Australia's equivalent of the Emmy) for Most Outstanding Actor in a Drama Series, for his lead roles in White Collar Blue and The Flying Doctors. Among his many other television credits are leads in Cardiac Arrest; The Knock; Deceit;(the U.K.'s) Queer as Folk; and Nightmares and Dreamscapes: From the Stories of Stephen King.

He has been nominated several additional times for Logie and Australian Film Institute (AFI) Awards. His feature credits include Craig Rosenberg's Hotel de Love; Richard Pearce's telefilm Fatal Contact; Sean Faughnan and Ezna Sans' Act of God; and Strathford Hamilton's The Pact.

On stage, Mr. O'Brien has starred in productions of A Doll's House, Butterflies Are Free, The Rivals, Macbeth, The Cherry Orchard, The Pirates of Penzance, and Arcadia, amongst many others.