Background
O'Neill was born in Belfast and was educated at the Royal Belfast Academical Institution.
O'Neill was born in Belfast and was educated at the Royal Belfast Academical Institution.
Guildford School of Acting.
He trained at the Guildford School of Acting. His first television role was in Extremely Dangerous (1999). His performances during the RSC's six-week residency at Park Avenue Armory in New York were hailed as "forceful" and "irresistible." At the 2012 World Shakespeare Festival in Stratford-upon-Avon, O'Neill played the title role in Roxana Silbert's production of Richard III at the Swan.
The Crucible by Arthur Miller, Royal Exchange Manchester (2015) for which he was nominated for a Manchester Award.
A member of the Royal Shakespeare Company (RSC) 2009-2011 ensemble, his roles included Mercutio in Romeo and Juliet, Orlando in As You Like It, and Launcelot in Morte D'Arthur.