Aside from releasing music as a recording artist, O'Halloran is a film and TV composer, as well as one half of ambient act A Winged Victory for the Sullen.

While studying art at Santa Monica College, he met singer Sara Lov, with whom he founded indie rock band Dévics in 1998.

He has since released three more solo records, the latest of which is Lumiere (2011), which featured contributions by Peter Broderick and Adam Wiltzie (Stars of the Lid), and was mixed by Jóhann Jóhannsson.

In 2014, O’Halloran worked on Indian drama Umrika, which won the Audience Award at Sundance, and gave him his first opportunity to compose for a full string orchestra.

[citation needed] In the same year he was also asked to provide the music for Transparent, the acclaimed TV series created by Jill Soloway for Amazon Studios.