Simon’s performances as Siegmund in Die Walküre at the Royal Opera House, Covent Garden with Pappano, Teatro alla Scala and Berlin Staatsoper with Barenboim, at the Metropolitan Opera with Runnicles in the celebrated Otto Schenk production returning with Luisi in the Lepage Ring Cycle and in the Götz Friedrich production at Deutsche Oper Berlin with Rattle were performed to wide critical acclaim. He was described in the international press as “an exemplary Siegmund, terrific of voice", "THE Wagnerian tenor of his generation" and "a turbo-charged tenor".

This season Simon makes his debut at Opera National de Paris and returns to the Bayerische Staatsoper as the title role in Parsifal with Young, Siegmund in Die Walküre for Oper Leipzig, the title role in Tristan und Isolde at Santa Fe Opera and Gaffigan, Florestan in Fidelio with the Sydney Symphony with Young, Boris in Katya Kabanova with the London Symphony Orchestra and Siegfried in concert with the Symphonieorchester des Bayerischen Rundfunk both with Rattle and then with Sinfonieorchester Basel and Elder.

Notable debuts have included; the Royal Opera House (2005) Jenik in The Bartered Bride with Mackerras, the Salzburg Festival (2005) in Die Zauberflöte with Muti, the Metropolitan Opera (2006) as the Gran Sacerdote in Idomeneo with Levine, Opera Australia (2009) as Sergei in Shostakovich's Lady Macbeth of Mtsensk with Armstrong, Siegmund in Die Walküre at Teatro alla Scala (2010), the Staatsoper unter den Linden, Berlin with Barenboim and the Bayerische Staatsoper with Nagano (2013), Chairman Mao in Nixon in China with Renes with the San Francisco Opera (2012), and the Wiener Staatsoper (2012) in the title role of Parsifal with Thielemann.

Notable engagements have included opening La Scala's season as Siegmund in Die Walküre with Barenboim and with the Wiener Staatsoper with Welser-Möst. He returned as Siegmund in the celebrated Keith Warner Royal Opera House, Covent Garden Ring Cycle where he also performed; Lohengrin, Fidelio, Stolzing in Die Meistersinger von Nürnberg and the title role of Parsifal. He made his debut with the Hallé Orchestra in the title role of Wagner’s Siegfried in concert with Sir Mark Elder at the Edinburgh Festival and with Jaap van Zweden with the Hong Kong Philharmonic - both these performances have been released on CD. He made his debut as Der Kaiser in Die Frau ohne Schatten at the Berlin Staatsoper with Simone Young and as the Tambourmajor in Wozzeck with Levine at the Metropolitan Opera.

Simon has appeared in many of the world’s leading concert halls including Carnegie Hall for Das Lied von der Erde with James Levine and The Met Orchestra and Missa Solemnis with the Boston Symphony, Florestan in Fidelio at both the Salzburg Festival and BBC Proms with Barenboim and with the National Symphony Orchestra and Eschenbach at the Kennedy Center, Gurrelieder in the BBC Proms at the Royal Albert Hall and Edinburgh Festival, Das Lied von der Erde, Fidelio and Parsifal in concert at Accademia Nazionale di Santa Cecilia with Pappano and Gatti, Parsifal Act 3 with Nelsons and the Bayerischer Rundfunks Orchestra at the Munich Herkulesaal, Der Freischütz with Sir Colin Davis and the London Symphony Orchestra, Janacek’s Glagolitic Mass with Dutoit at Tokyo’s NHK Hall and with Boulez in the BBC Proms at the Royal Albert Hall, Mahler’s Symphony No. 8 at the Sydney Opera House with Ashkenazy and Beethoven’s Symphony No.9 for the reopening of London’s Royal Festival Hall. He also had the honour of touring Europe with Daniel Barenboim and the West-Eastern Divan Orchestra performing Act I Die Walküre in concert, performing complete the Ring Cycle with the Staatskapelle Berlin with Barenboim at the BBC Proms and Act 1 in concert with the Berlin Philharmonic and Sir Simon Rattle at the Philharmonie. Simon made his debut with the New York Philharmonic as Siegmund in Die Walküre Act one in concert with Jaap van Zweden.

His discography includes his ‘Best Classical Tui’ award winning lieder CD is titled Distant Beloved with pianist Terence Dennis and the Decca label; his debut solo award winning album; Father and Son, Wagner Scenes and Arias (Lohengrin, Parsifal, Siegmund and Siegfried) with Pietari Inkinen and the NZSO for EMI. He also appears in the title role of Siegfried in the Jaap van Zweden Ring Cycle recording for Naxos and with the Hallé Orchestra and Sir Mark Elder, Die Walküre on Blu[1]ray and DVD with Daniel Barenboim from La Scala, the title role of Parsifal on Blu-ray and DVD with Sir Antonio Pappano from Covent Garden, the title role of Otello and Max in Der Freischütz with Sir Colin Davis for LSO Live, Die Zauberflöte for the Salzburg Festival Mozart 25 DVD with Riccardo Muti, Mahler’s Symphony No.8 with Valery Gergiev and the Munich Philharmonic and with Vladimir Ashkenanzy and the Sydney Symphony, Beethoven Symphony No.9 with Deutsche Kammerphilharmonie and Paavo Järvi and the Montreal Symphony Orchestra with Kent Nagano, Frank Martin’s Der Sturm with the Netherlands Radio Symphony and Thierry Fischer, Chauson’s Le Roi Arthus with Leon Botstein and the BBC Symphony Orchestra and most recently Voices of German Opera from EMI. Simon contributed as tenor soloist to the Deutsche Grammophon recording of Mahler's Symphony No.8 with the Los Angeles Philharmonic. The recording won the Grammy Award for Best Choral Performance.

Simon became an Officer of New Zealand Order of Merit in the 2017 Queen’s Birthday Honours list, he is an alumnus and holds a Doctor of Music (Honoris Causa) from Victoria University of Wellington and is an alumnus of the University of Otago, the Manhattan School of Music and the Juilliard Opera Center. He is a Fulbright Scholar, was awarded the 2005 Arts Laureate of New Zealand and was a grand finalist in the 2002 Metropolitan Opera National Auditions returning as guest artist in 2007. He also appears on the 1998 New Zealand one-dollar performing arts postage stamp.