Highlights of recent seasons include his debut at the Opéra National de Paris as Parsifal, which he also interpreted at the Bavarian State Opera, Tristan at Santa Fe Opera, Florestan with the Sydney Symphony under Simone Young, Boris in Katya Kabanova with the London Symphony Orchestra, and Siegfried in concert with the Bavarian Radio Symphony Orchestra under Simon Rattle and with the Basel Symphony Orchestra under Mark Elder.
O’Neill has worked with outstanding conductors including Antonio Pappano, Riccardo Muti, Pierre Boulez, Fabio Luisi, Donald Runnicles, Christian Thielemann, Jaap van Zweden, Daniel Harding, Esa-Pekka Salonen, and Gustavo Dudamel.

His broad concert repertoire, which includes Mahler’s Lied von der Erde and the Eighth Symphony, Beethoven’s Missa Solemnis and the Ninth Symphony, Janáček’s Glagolitic Mass, and Schoenberg’s Gurrelieder, has taken him to the world’s most prestigious concert halls, including Carnegie Hall in New York, the Royal Albert and Royal Festival Hall in London, the Accademia Nazionale di Santa Cecilia in Rome, and the NHK Hall in Tokyo.

O’Neill’s discography includes recordings for the Decca, Warner, Naxos, and LSO Live labels. He is a graduate of and holds a Doctor (h.c.) of Music from Victoria University of Wellington and a graduate of the University of Otago, Manhattan School of Music, and Juilliard Opera Center. His portrait graced the 1998 New Zealand one-dollar stamp.