Described as “THE Wagnerian tenor of his generation”, Simon O'Neill has appeared at the Metropolitan Opera, Royal Opera House Covent Garden, Teatro alla Scala in Milan, Deutsche Staatsoper and Deutsche Oper, Staatsoper of Vienna as well as the Bayreuth, Ravinia and Salzburg festivals. He sang under the directions of conductors such as James Levine, Riccardo Muti, Sir Simon Rattle, Valery Gergiev, Thomas Hengelbrock, Sir Donald Runnicles, James Conlon, Antonio Pappano, Esa-Pekka Salonen, Jaap van Zweden and Christian Thielemann.
Simon O'Neil has performed Siegmund (Covent Garden), Stolzing (Covent Garden), Lohengrin (Covent Garden, Bayreuth), Florestan (Covent Garden, Salzburg Festival) and Parsifal (Covent Garden, Vienna, Madrid, Bayerischer Staatsoper), Siegmund, (Metropolitan Opera, Hamburg, La Scala, Berlin, Vienna, Munich), Cavaradossi (Hamburg, Tokyo, Berlin), Tambour Major (Wozzeck, Metropolitan Opera), Max (Der Freischutz, London Symphony Orchestra), Mao (Nixon in China, San Francisco), Otello (New Zealand Opera, Houston), Erik (Der Fliegende Holländer, Ravinia Festival), the title role Siegfried (with Jaap van Zweden and the Gurrelieder at the BBC Prom, at the Edinburgh Festival in conducted by Sir Mark Elder). His engagements include Mahler's Symphony No. 8 with Daniel Harding at the BBC Proms in 2018, Das Lied von der Erde with the London Symphony Orchestra and Simon Rattle, Boris in Katya Kabanova (Deutsche Staatsoper), Siegmund with Petrenko, Götterdämmerung in Houston, Tambour-Major in Hamburg.