One of the leading baritones of the 20th century and particularly associated with the French and Italian repertoires, he was considered a fine singing actor equally at home in dramatic or comic roles and gave regular song recitals.

[2] As a teenager he took voice lessons with a Madame Bastard in Béziers in his free time and made his operatic debut during the war as Ourrias in Gounod's Mireille[2] in the town arena.

[6] He joined the opera company of José Beckmans in 1950, and was a member of La Monnaie in Brussels from 1953 until 1956,[3] making his debut in the title role of Rossini's Il barbiere di Siviglia.

[4] There he sang the French repertory, both in opera (Gounod's Faust, Delibes' Lakmé, Massenet's Manon and Werther) and in operetta (Angélique, La belle Hélène, Les cloches de Corneville, Miss Heylett, Monsieur Beaucaire).

[9] While at the Monnaie, the French soprano Martha Angelici, whose husband was François Agostini, director of the Opéra-Comique at the time, sang in Les pêcheurs de perles with him; she suggested that he audition for the Paris company, which accepted him.

From 1964 he appeared at the Royal Opera House in London, where his roles included Sir Richard Forth in Bellini's I puritani alongside Joan Sutherland in 1964, Almaviva in 1965, Scarpia in 1966, Malatesta in Donizetti's Don Pasquale in 1973, Doctor Bartolo in Il barbiere in 1975, and Golaud in Debussy's Pelléas et Mélisande in 1982.

[10][15] He also sang frequently at the Philadelphia Lyric Opera Company between 1963 and 1968, making his debut on 22 February 1963 as Zurga in Bizet's Les pêcheurs de perles with Ferruccio Tagliavini as Nadir and Adriana Maliponte as Leïla.

[20] In 1975 a critic reviewing Donizettis's L'elisir d'amore commented that "broad humour is quite foreign to Bacquier's nature ... his doctor [Dulcamara] is a serious Archie Rice type, no caricature but a real man weighed down by his own charlatanism and basically sad that mankind is so gullible".

[21] Rare tentatives in non-French and Italian repertoire came with Wolfram in Tannhäuser by Wagner, praised by André Pernet,[10] and the title role in Boris Godunov by Mussorgsky in 1971[22] (both sung in French translation).

Bacquier also created the title roles of Jean-Pierre Rivière's Pour un Don Quichotte at La Piccola Scala [it] (Milan) on 10 March 1961,[4] and Daniel-Lesur's Andréa del Sarto at the Opéra de Marseille in 1969, where one critic wrote "...rarely has a singer shown such complete mastery, both as a vocalist and as an actor.

[30] He was also active in the field of mélodies, and made recordings of songs by Maurice Ravel, Déodat de Séverac, Marc Berthomieu, Francis Poulenc and others.

He is featured as one of the interviewees in the book by Sylvie Milhau Doucement les Basses ossia Dîner avec Gabriel Bacquier, José van Dam et Claudio Desderi.

[33] He was one of the lead signatories to a petition in 2008 Appel à la Refondation des Troupes de Théâtre Lyrique to defend and promote French singing.