Souzay entered the Paris Conservatoire in 1940, studying with Claire Croiza and Jean-Emil Vanni-Marcoux. He actually began singing as a tenor, but in 1943, with advice from the leading operatic singer Henri Etcheverry, he became a baritone. He graduated from the Conservatoire in 1945 with two first prizes, the Prix de chant and the Prix de vocalise. While at the Conservatoire, he also tried his hand at composition and in 1942 three of his settings of poems by Paul Valéry were given a performance by Pierre Bernac. He went on to study voice with Bernac, although he subsequently expressed some differences with the latter's methods and ideas on pronunciation. He was eager not to limit himself to being a specialist in the French repertoire, and he made a detailed study of German lieder with Lotte Lehmann.
Souzay's exceptional linguistic gifts enabled him to sing convincingly in 13 different languages including Hebrew, Portuguese and Russian. In contemporary music he performed in Honegger's La danse des morts and in the world première of Stravinsky's Canticum sacrum. The composer Jacques Leguerney (1906-1997) wrote many songs for Souzay and for his sister.
His operatic career began in 1947 in Cimarosa's Il matrimonio segreto at the Festival d'Aix-en-Provence, but it was not until the late 1950s that he extended his stage work - though even then it did not take precedence over his recitals. His roles included Monteverdi's Orfeo, Mozart's Don Giovanni and Almaviva in The Marriage of Figaro, Lescaut in Massenet's Manon, and Méphistophélès in Berlioz's La damnation de Faust. One of his favorite and most successful roles was Golaud in Debussy's Pelléas et Mélisande.
He did little operatic work after the 1960s, but continued his recital career, finally retiring from performance in the late 1980s. He spent the last years of his life giving master classes in the United States, Europe and Japan: he was an inspiring teacher, preferring to work on phrasing and the mood of a song rather than French diction.
He was a keen abstract painter, and in 1983 he published a book Sur mon chemin: pensées et dessins in which a selection of his paintings was accompanied by his written commentary, on art and life. He died at his home in Antibes in the south of France on 17 August 2004.
The New York Times described his voice as "not huge, but rich in color and tone, supple and sensual and lovely." Souzay was "a sensualist, reacting viscerally to the music and allowing it to carry him in new directions in a given concert."
The Guardian judged that "the basis of his popularity in recital lay in his easily produced, vibrant, warm baritone. It was used by its owner with an innate sensibility and an unfaltering sense of style. His attractive art was founded, above all, on a very French approach, at once balanced and urbane, yet inwardly poetic."
In the 1950s, Souzay's style of singing became the object of some unexpected criticism when it was cited by Roland Barthes in one of his essays in Mythologies, "L'art vocal bourgeois". Referring to a recording of Fauré songs, Barthes complained that Souzay invested particular words with superfluous emotion by means of an exaggerated phonetic dramatisation, and that by imposing his own "signs" of emotion he stifled the meaning of the words and music. Not everyone has agreed with Barthes's description of the style, let alone with the force of his argument, but these are strictures which would attach to many other singers besides Souzay and go to the heart of how vocal performance should be approached. (Indeed some years later, Barthes made similar criticisms against the singing of Dietrich Fischer-Dieskau. )
Souzay regarded himself as a romantic. Never analytical or detached in his performances, he said: "For me music is limpid and speaks for itself. I can only offer my emotions when I sing".
A. Blyth, ed. Song on Record 2. (Cambridge University Press, 1988).