Ruairí studied television and film production before attending the Institute of Art, Design and Technology in Dún Laoghaire, Ireland, graduating in 1996. He began his career with entry-level work on film sets, including work on Far and Away (1992), before gaining experience as a camera operator on documentary productions in Romania.
After working on factual television and short films in Ireland, O’Brien moved into scripted television drama. Director Colm McCarthy hired him as director of photography on the BBC series Murphy’s Law, helping establish his career in television. He went on to work on a range of British and Irish productions, including The Tudors, The Musketeers, Moone Boy and A Touch of Cloth.
O’Brien’s television credits include Line of Duty, The Fall, Humans, The A Word, In Plain Sight and Vigil. His work on The Fall earned him an Irish Film and Television Award nomination for Best Director of Photography in Film or Television Drama. He has also worked on feature films including Five Minutes of Heaven (2009), Sea Fever (2019), Dating Amber (2020), The Winter Lake (2020) and Jericho Ridge (2023).
His later television work includes The One, The Power and We Were the Lucky Ones. He also served as director of photography on Small Town, Big Story, a television series created by Chris O’Dowd.