Amedeo Tommasi was born in Trieste on 1 December 1935. He began classical piano lessons at six, interrupted for several years by the Second World War, and resumed formal study between 1946 and 1950, discovering jazz as a boy through Allied radio broadcasts; pianist George Shearing was an early model he taught himself to imitate by ear.

Around 1952 he moved to Bologna to attend university and instead found the city's jazz scene through the "Disclub" record shop. Before committing to modern jazz he played trombone in the Dixieland "Panigal Jazz Band" of Bologna. He then formed a modern-jazz trio with bassist Maurizio Maiorana and drummer Mario Camassa, and in 1959 the group placed third among modern-style bands in "La Coppa del Jazz," a national competition run by state broadcaster RAI. The trio's 1960 album Zamboni 22 - genre-tagged Hard Bop and Afro-Cuban Jazz, and named for a Bologna street - carries several of his own compositions, including "Ballata in Forma di Blues," "Ballad for Micheline" and "Autostrada del Sole." A string of 1961 festival dates followed: St. Vincent, Comblain-la-Tour in Belgium, and the Sanremo festival, plus first prize in the small-ensemble category at Yugoslavia's Bled Festival, where Modern Jazz Quartet pianist John Lewis congratulated him in person.

In 1961 Tommasi joined the European touring band American trumpeter Chet Baker assembled after his release from an Italian prison, alongside Belgian saxophonist/flutist Bobby Jaspar and guitarist René Thomas. The resulting album, Chet Is Back! (RCA Victor, recorded January 1962 at RCA Italiana's Rome studios), carries a new recording of Tommasi's own "Ballata in Forma di Blues" and is the best-known credit of his jazz career. He also recorded separately as part of the Thomas-Jaspar Quintet the same year, and worked with visiting Americans Buddy Collette and Conte Candoli. He later said the difficulty of sustaining a jazz career in 1960s Italy was exactly why he left Bologna for Rome.

A trio session Tommasi led in Rome on 13 July 1967, entirely original material, went unreleased for more than four decades before surfacing as Blues for Miles Davis (Cinedelic Records, 2010); one track, "Rene' and Bobby," is named for his two Chet Baker-group bandmates.

From the late 1960s Tommasi built a second, far larger career composing for film, television and production ("library") music, starting with the score for I lunghi giorni dell'odio (1968). He scored several early features for director Pupi Avati, including Balsamus, l'uomo di Satana (1968), Thomas (1970) and La mazurka del barone, della santa e del fico fiorone (1975); the dissonant, unsettling score he wrote for Avati's giallo horror film La casa dalle finestre che ridono (1976) is cited by genre historians as a template for the classic giallo sound. Alongside soundtrack work he became a prolific library-music composer - releasing library LPs such as Carnet Turistico, Zodiac and Ittiologia (1970-73) - and, into the 1980s, scored Italian public-television science documentaries including RAI's long-running Il Mondo di Quark. For the Italian dub of the American soap opera Santa Barbara, he composed new Italian-language opening and closing themes plus original incidental music replacing the U.S. score, across roughly the first 1,000 dubbed episodes. He worked repeatedly alongside fellow Italian library-music composers Alessandro Alessandroni, Stefano Torossi, Gerardo Iacoucci and Sandro Brugnolini.

In 1998 he contributed to Ennio Morricone's score for Giuseppe Tornatore's The Legend of 1900 (La leggenda del pianista sull'oceano): he performed piano on the soundtrack, is credited with two pieces within the score - "Magic Waltz" and "Danny's Blues" - and appeared on screen in a small role as a piano tuner.

Tommasi taught jazz harmony for many years at Rome's Saint Louis College of Music, developing his own teaching method built around the reharmonization of American standards, and spent five years directing ear-training and harmony courses at the Siena Jazz summer school; in 1992 he also taught a summer course for classical-composition students at Siena's Accademia Chigiana. He continued teaching at Saint Louis until his death in Rome on 14 April 2021, at 85.

Tommasi's 1960s jazz work sits inside the cool, chamber-scaled European bebop that defined Chet Baker's post-prison European recordings: light-toned, harmonically alert small-group playing built for a sextet rather than a big band, with his own writing - "Ballata in Forma di Blues," the trio pieces later issued as Blues for Miles Davis - staying inside that same conversational, mid-tempo idiom, while Zamboni 22's Discogs styling (Hard Bop, Afro-Cuban Jazz) shows a harder-edged, more rhythmically active side of the same trio book. His early self-taught model was George Shearing's block-chord style, filtered through classical training begun in childhood.

His much longer second career, in film and library music, pulled that same harmonic fluency toward orchestral and electronic textures: dissonant, unsettling writing for Pupi Avati's horror films sits alongside brighter production-music cues for Italian television and early experiments with synthesizers on his library LPs - a jazz-trained harmonic ear applied to a classical-scaled, screen-facing idiom, the reasoning behind this profile's "Third Stream" tag. Press retrospectives written after his death describe him as a quietly influential figure in Italian jazz whose standing among musicians outpaced his renown with the wider public - a pianist's pianist first, a soundtrack craftsman second.