Gismonti was born in the small city of Carmo, state of Rio de Janeiro, Brazil, into a musical family. His mother was from Sicily and his father was from Beirut, Lebanon. At the age of six, he started studying the piano at the Brazilian Conservatory of Music. After studying the classical repertoire in Brazil for fifteen years, he went to Paris to delve into modern music. He studied with Nadia Boulanger (1887–1979), after acceptance as a student by the composer Jean Barraqué, a student of Anton Webern and Schoenberg. Boulanger encouraged Gismonti to write the collective Brazilian experience into his music.