Performed operatic roles include: Musetta: La bohème (Berlin Italian Opera); Frasquita (understudy): Carmen, Papagena (understudy), Zweite Knabe (understudy): Die Zauberflöte (New Zealand Opera); Despina: Cosi fan Tutte (Wanderlust Opera; Days Bay Opera); Lieschen: Coffee Cantata (Wanaka Arts Festival); Linfea: La Calisto, Annina: Der Rosenkavalier, Auretta: L’oca del Cairo (Days Bay Opera); Mercedes: Carmen (New Zealand Choral Federation); Hermia: A Midsummer Night’s Dream (New Zealand School of Music).
An accomplished character actor, Imogen has often been cast in comic soubrette roles. Praised for her stylish delivery of a quirky and vivacious Despina in Cosi fan tutte (Opera News), Imogen’s first incarnation of the role, for Days Bay Opera, was described as “bubbling with a mix of infectious energy and insouciance which made her a force to be reckoned with beneath the girlishness!” (Middle C). Imogen went on to perform in a touring production with Wanderlust Opera, an initiative bringing quality performances of opera to New Zealand audiences outside of major centres. Her Despina was, again, favourably reviewed: “Imogen Thirlwall's performance as Despina the meddling maid was outstanding with incredible stage presence and vocals to match.” (Taranaki Daily News).
Imogen has performed in six productions with Days Bay Opera, situating opera at Canna House surrounded by native beech forest. In Cavalli: La Calisto, “Linfea’s thoughts ran the full gamut of the lovesick maiden’s thoughts and feelings in a totally convincing fashion” (Radio New Zealand). Imogen used her “comic talent and gift for characterisation to great effect” as Annina in Strauss: Der Rosenkavalier (Seen and Heard International). As maidservant Auretta in Mozart: L’oca del Cairo, “Imogen Thirlwall and Christian Thurston often stole the scene as the marquis’s inevitable servants” (The Listener); Imogen was described as “an absolute delight, voice production and stage movement so spontaneously “theatrical” in overall impulse one felt in complete and more-or-less instant accord with the character” (Middle C).
For the Wanaka Arts Festival, Imogen performed the role of Lieschen in Bach: Coffee Cantata with the New Zealand Trio, presenting a midday traditional version and a 10pm burlesque version; “this taste of an opera… a hilarious and exquisite half hour, showcasing an artform many shy away from” (The Wanaka Sun).
In February 2018, Imogen made her European debut as Musetta in La bohème with Berlin Italian Opera at Theater Morgenstern.
Concert repertoire includes Saint-Saëns: Oratorio de Noël, Mozart: Requiem Mass, Faure: Requiem, Mendelssohn: Symphony No. 2 Hymn of Praise, Mozart: Vesperae solennes de confessore, Haydn: Nelson Mass, Bach: Christmas Oratorio, and Schubert: Mass in C Minor.
Known for her adventurous and passionate approach to modern repertoire, Imogen performed as soprano soloist for Will Todd: Mass in Blue in her hometowns of Wellington and Tauranga; "Imogen Thirlwall soared above the choir and trio, thrilling the audience with the clarity, power and beauty of her voice. Her command of the jazz idiom was breath taking and a credit to her musicality and versatility" (John Wanhill).
She also performed in the southern hemisphere premiere of Robert Hanson’s oratorio, Hiawatha. Hanson, who was in attendance, wrote to Imogen: “as a gifted soprano and a gifted musician… intonation impeccable, preparation wonderful and the dramatic elements set a new standard for the role of Minnehaha”.