O'Neill resides in Wellington, New Zealand. He has participated in both theatre and film, and recently resumed his acting career after a long period of working as a boilermaker.
He did over 40 days as an extra for both The Desolation of Smaug and The Battle of Five Armies (2012-13). He was also Chopper Dwarf in The Esgaroth Three's music video parody "Dwarf on a Pig". At the Rivendell Archway official opening ceremony in 2015, he portrayed Gandalf in a re-enactment of the "You shall not pass!" scene.