He was studying art at the Santa Monica College. O’Halloran first received widespread recognition after Sofia Coppola invited him to contribute music to her award-winning Marie Antoinette. O’Halloran’s solo piano pieces provided the movie moments of eloquent stillness.As a part of indie rock band Dévics he recorded five albums and though they are not performing together anymore, the band actually never split up. By the time their last release, Push The Heart, O’Halloran already had two albums of solo piano pieces recorded, Piano Solos Vol. 1 (2004) and Vol. 2 (2006), and has gone on to score a number of films and TV shows. These resulted in an Oscar and Golden Globe nomination. O’Halloran worked together with Volker Bertelmann on Lion (2016) and The Current War (2017). He also scored In the Shadow of Iris (2016) and God’s Own Country (2017) as A Winged Victory for the Sullen.