Fernández studied at the Instituto Nacional de Música with Francisco Braga, Frederico Nascimento, and Henrique Oswald. In 1923, Nascimento was taken seriously ill, and Fernández was designated his temporary substitute in the chair of upper-level harmony, an appointment which became permanent two years later (Kiefer 1986, 81). In 1936 he founded the Conservatório Brasileiro de Música in Rio de Janeiro, which he directed until his death. From 1939 onward, he also served as Professor of Choral Singing at the Conservatório Nacional de Canto Orfeônico.
He composed a three-act opera, Malazarte (1931–33), to a libretto by José Pereira Graça Aranha, who adapted it from his own play of the same title. For the premiere at the Teatro Municipal, Rio de Janeiro, 1941), the libretto was translated into Italian. Malazarte is a nationalist work in both its subject matter and its musical content, and is considered the first successful Brazilian opera of this type (Béhague 2001). In 1941 Fernández extracted a three-movement suite from the opera, the last movement of which, "Batuque" (an Afro-Brazilian folk dance), became very popular. He also composed one ballet, two symphonies, five symphonic poems, two orchestral suites, one concerto each for piano and for violin, chamber music, about 80 compositions for piano, choral music, and 36 songs.
Baumann, Simpson de Brito Melo. 1998. "O nacionalismo musical nas três suítes brasileiras de Oscar Lorenzo Fernandez". In Anais do I Simpósio Latino-Americano de Musicologia, edited by Elisabeth Seraphim Prosser and Paulo Castagna. Curitiba: Fundação Cultural.
Béhague, Gerard. 1979. Music in Latin America: An Introduction. Prentice-Hall History of Music Series. Englewood Cliffs, NJ: Prentice-Hall. ISBN 0-13-608919-4 (cloth) ISBN 0-13-608901-1 (pbk.)
Béhague, Gerard. 2001. "Fernândez, Oscar Lorenzo". The New Grove Dictionary of Music and Musicians, edited by Stanley Sadie and John Tyrrell. London: Macmillan; New York: Grove’s Dictionaries.
Kiefer, Bruno. 1986. "Oscar Lorenzo Fernandez: Música para piano solo, canções para voz e piano". Latin American Music Review/Revista de Música Latinoamericana 7, no. 1 (Spring-Summer): 81–98.