Giovanni Tommaso grew up in a house that already had jazz in it. His brother Vito played piano in the Quintetto di Lucca, the group a teenage Giovanni joined in 1957, and the band won La Coppa del Jazz, a national RAI radio jazz competition, the following year. At 18, cruise-ship orchestra work took him through New York in 1959 and 1960, where he sat in rooms watching Paul Chambers, Ray Brown, and Charles Mingus play. By 1962 he was touring Italy and Europe with Chet Baker, alongside pianist Amedeo Tommasi and drummer Franco Mondini.

In 1967 he moved to Rome and spent nearly four years as a staff instrumentalist, arranger, and producer at RCA Italiana, working sessions behind Riccardo Cocciante, Mina, Gianni Morandi, Rino Gaetano, and Ivan Graziani. Then he heard Miles Davis's Bitches Brew, and the acoustic, session-player track he was on no longer felt like enough. He gathered pianist Franco D'Andrea, saxophonist Claudio Fasoli, drummer Bruno Biriaco, and guitarist Tony Sidney at his own apartment on Via Beato Angelico in Rome, and Perigeo was born in 1971/72.

From 1972 to 1977, Perigeo released nine studio albums on RCA Italiana, fusing jazz-rock with a distinctly Italian melodic sensibility, and toured Italy, France, the UK, Canada, the US, and Switzerland. The catalog includes Azimut (1972), Abbiamo Tutti Un Blues Da Piangere (1973), Via Beato Angelico and Genealogia (both 1974), La Valle Dei Templi (1975), Non È Poi Così Lontano (1976), and Fata Morgana and Attraverso Il Perigeo (both 1977).

Tommaso's studio-arranger instincts never left him. He co-wrote the score for Pupi Avati's Ma quando arrivano le ragazze? with Riz Ortolani, and the soundtrack won Italy's David di Donatello award.

After Perigeo wound down, Tommaso kept building bands under his own name rather than just joining them. The Giovanni Tommaso Quintet released Via G.T. (1986) and To Chet (1988), the latter a Chet Baker tribute pulling together trumpeters Paolo Fresu and Flavio Boltro, pianist Danilo Rea, and drummer Roberto Gatto, followed by Over the Ocean (1993), Strane Stelle Strane (1995), and Third Step - Good Bye 900 (1998). In 2000 he co-led La Dolce Vita with Enrico Rava as the Tommaso/Rava Quartet, and its 2001 follow-up, Secondo Tempo, brought in Joe Lovano, Terri Lyne Carrington, and Antonio Faraò as guests. In 2007 he founded a new group, Apogeo, releasing Codice 5 in 2010, and in 2011 formed the trio Basso Profilo with clarinetist Gabriele Mirabassi and accordionist Simone Zanchini.

He has kept the pace of new work into his eighties. Walking in My Shadow, from 2023, puts Rita Marcotulli on piano alongside saxophonist Javier Girotto and drummer Alessandro Paternesi, reaching back through Tommaso's own catalog, from 1966's "White Keys" to 2009's "Codice 5," to find new shapes for songs he wrote decades apart.

Since 1986 Tommaso has directed the Umbria Jazz Clinics seminars and held the jazz chair at the Perugia Conservatory; he also teaches at CEMM in Milan. In 2003, Berklee College of Music gave him an honorary doctorate on the Umbria Jazz Festival stage.

Tommaso's playing bridges two distinct traditions rather than choosing between them: the acoustic post-bop lineage he absorbed firsthand from watching Paul Chambers, Ray Brown, and Charles Mingus in New York clubs as a teenager, and the electric jazz-rock language he adopted wholesale after hearing Miles Davis's Bitches Brew in 1971. Perigeo's catalog carries an unusually Italian melodic identity inside a fusion frame, closer in spirit to Weather Report's compositional ambition than to a straight funk-jazz crossover. His later Quintet work, especially the Chet Baker tribute To Chet, pulls back toward a warmer, more lyrical post-bop sound built around working relationships with trumpeters Paolo Fresu and Flavio Boltro. As a composer and arranger, his RCA Italiana production years and his David di Donatello-winning film score work with Riz Ortolani show the same studio discipline that runs underneath his jazz leader dates.