Mendes was born in Santos. He attended the Santos Conservatory from 1941 to 1949, and studied composition under Cláudio Santoro in 1954 and under George Olivier Toni from 1958-1960. In the 1960s he studied in Darmstadt under Pierre Boulez, Henri Pousseur, and Karlheinz Stockhausen. Mendes's compositions include cantatas, motets, orchestral music, incidental music, solo and chamber pieces, and some avant-garde works. Most of them are published by Alain Van Kerckhoven Editeur. In 1965, he founded the Santos New Music Festival. In the 1970s and 1980s, he taught at the University of Wisconsin–Madison and the University of Texas, then was professor of music in São Paulo.
VIDEO: 47° Festival Música Nova- Gilberto Mendes Quarteto de Cordas Brasileiro de Tel Aviv Violinos: Abner Landim, Simone Elenciuc Viola: José Batista Junior Cello: Emerson Nazario Piano: Rodrigo Antonio Silva Gilberto Mendes-1922-2016 Rimsky Piano quintet-2003 Ribeirão Preto, 26 de setembro 2013