After leaving school O’Hara first joined a youth opportunities programme at Glasgow Arts Centre, which saw him tour schools in theatre productions, before moving temporarily to London to study at the Central School of Speech and Drama. During his time at the Central School of Speech and Drama, he returned to Glasgow to take on his first screen role – in Bill Forsyth’s 1984 film Comfort And Joy.
The career that has followed has spanned television on both sides of the Atlantic, including The Tudors, Prime Suspect V and Taggart, and likewise UK and American cinema. O’Hara’s movie credits include Cowboys & Aliens, Wanted and The Departed. He is no stranger to villainous roles, such as those of Albert Runcorn in Harry Potter And The Deathly Hallows: Part 1 and the shadowy government figure Michael Canaris in Glasgow-set Doomsday, however in perhaps his best known role he is one of the good guys – the insane Irish character Stephen in Braveheart.