Musically self-taught, he worked primarily in theatre composition before forming seminal Dublin psych-rock band The Jimmy Cake. A graduate of Trinity College, Dublin, where he studied with composers Donnacha Dennehy and Kevin Volans, O’Connor has for many years worked primarily in a tonal, minimal palette, writing for chamber ensembles and solo musicians. His most recent song cycle, Left Behind – commissioned by vocalist Michelle O’Rourke – formed the centrepiece of the Irish Republic’s International Women’s Day Centenary Celebrations in 2016.