In 1929, Nash made his debut at the Royal Opera House, Covent Garden as Don Ottavio in "Don Giovanni" in the company's International Season. He sang leading tenor roles in Italian and French operas at Covent Garden until World War II, including Almaviva, Pinkerton, Faust, Roméo, Rodolfo in "La bohème", Eisenstein in "Die Fledermaus", Rinuccio in "Gianni Schicchi", and Pedrillo in "Die Entführung aus dem Serail". The critic Alan Blyth called Nash the leading British lyric tenor of the 20th century, and considered him "ideal casting for the heroes of French 19th-century Romantic opera." Nash had a repertoire of twenty-four operas, and sang fluently in English, French, German and Italian. He was proud of being the first Englishman to sing David in "Die Meistersinger" in the International Season at Covent Garden.