At 19, he decided to dedicate himself to music as a profession, being invited to join Gilberto Gil's band in 1981, with which Fonseca played throughout Brazil and in several other countries. Fonseca also has played and recorded with Chico Buarque, Djavan, Milton Nascimento, Caetano Veloso, Gal Costa, Elza Soares, Marisa Monte, João Bosco, Jorge Benjor, Leila Pinheiro, Simone, and others. His resumé includes several international tours, four performances at the Montreux Fest (Switzerland) and other festivals around Europe, Canada, U.S., and Japan. In 1986, he became a producer, working for Vinícius Cantuária. Fonseca also produced Gil's O Eterno Deus Mu Dança, Daúde's debut album (that brought him the Sharp Prize as the best pop/rock arranger of 1996), the two first solo albums by Virgínia Rodrigues, six tracks of Leo Gandelman's Brazilian Soul, and Gal Costa's Aquele Frevo Axé, among other albums by Rosana, Adriana Maciel, Verônica Sabino, Daúde, and Zeca Baleiro.

Minha Cara, his first solo album, was released in 1986. O Som do Sim, the second, launched in Europe in 1995, hit number nine of the European world music chart.

In 1998, Gil's Quanta Live, which included Fonseca's participation, won the World Music Grammy. In the next year, Fonseca did the musical direction of the show Since Samba Has Been Samba at the Royal Albert Hall, London, with Gil, Caetano Veloso, Gal Costa, Chico Buarque, Elza Soares, and Virgínia Rodrigues. He participated also in Bebel Gilberto's Tanto Tempo.

Fonseca's songs have been recorded by Caetano Veloso, Gal Costa ("Sorte," written with Ronaldo Bastos), Gilberto Gil, Maria Bethânia ("Sei de Cor," with Ronaldo Bastos), Ney Matogrosso ("Um Rei," with Ronaldo Bastos), Nana Caymmi ("A Noite É Meu Ópio" and "Flor Lunar," with Ronaldo Bastos), Milton Nascimento, Carlinhos Brown, Daúde, Vinícius Cantuária, Verônica Sabino, Adriana Maciel, Zizi Possi ("Mania," with Ronaldo Bastos), and Belô Velloso ("Polaróides," with Ronaldo Bastos). ~ Alvaro Neder