In the 1980s, O'Mahony was the lead singer for hardcore straight edge band No For An Answer (NFAA). The band is credited with being one of the cornerstones of the straight edge movement on the west coast and was the first west coast release by the prominent independent label Revelation Records. Later O'Mahony recorded records as the lead singer of bands such as Carry Nation, Voicebox, Speak 714, John Henry Holiday, God Forgot, and 411, which released the album This Isn't Me in 1991. In all, he sang on 16 records not counting assorted compilations and numerous live releases. Throughout his career, O'Mahony was known for the heavily activist nature of his lyrics espousing the rejection of homophobia, domestic abuse, the First Gulf War, and many self-destructive behaviors. In 1996 O'Mahony began experimenting with spoken word, organizing performances with Kevin Seconds and Sam McPheeters.