Possessing a warm lyrical voice with a considerable amount of flexibility and stamina, Duval sang mostly roles from the standard French and Italian repertories.
The following year he made his European debut as the Fisherman in Igor Stravinsky's Le Rossignol at the Teatro dell'Opera di Roma to great acclaim.
Duval had a major triumph in 1963, drawing international recognition for his lauded recording of the role of Arturo in Bellini's I puritani, opposite Joan Sutherland, after replacing Franco Corelli as a last minute substitute.
He sang several more time with the NYCO during his career, including portraying Rinuccio in Giacomo Puccini's Gianni Schicchi (1965), Le Chevalier des Grieux in Jules Massenet's Manon (1969), the Duke of Mantua in Rigoletto (1969), and Arturo to Beverly Sill's Elvira in Vincenzo Bellini's I Puritani (1974–1975) among others.
In 1969 he made his first appearance with the Philadelphia Grand Opera Company as Edgardo in Gaetano Donizetti's Lucia di Lammermoor with Roberta Peters in the title role.
He notably took part in a number of CBC opera telecasts, including portraying Macduff in Macbeth, in 1973, opposite Louis Quilico and Marisa Galvany.