Mark O'Brien

Mark O’Brien (born May 7, 1984) is a Canadian screen actor and director from St. John’s, Newfoundland and Labrador. Known for grounded, character-driven performances, he has built a career that moves comfortably between independent cinema and prestige television.

O’Brien first drew wide attention in Canada for his work as Des Courtney on Republic of Doyle (2010), where his naturalistic style helped make the series a standout. He later reached international audiences as Tom Rendon on AMC’s Halt and Catch Fire (2014), bringing emotional depth to a drama defined by ambition, technology, and shifting relationships.

On film, O’Brien’s credits span intimate dramas and genre storytelling, including Grown Up Movie Star (as Will), The Four Horsemen (as Eric Rollins), and Seven Veils (as Paul). He has also appeared in titles such as The Dark Stranger, Shadow of God, and Cut from the Same Cloth, continuing to expand his range across tones and formats.