Umberto Fiorentino was born in Rome on February 5, 1956, and has lived his entire life in and around the city. He is entirely self-taught: by his own account, hearing a high-school classmate play pieces by John McLaughlin and George Benson was "a shock" that sent him toward jazz. He began performing professionally on the Rome jazz club circuit in the mid-1970s, playing alongside musicians of his own generation before joining the groups led by drummer Roberto Gatto and saxophonist Maurizio Giammarco.

Those groups were a prelude to Lingomania, the electric jazz quintet Giammarco founded in 1984. Across its active years the band's lineup included Gatto on drums, trumpeter Flavio Boltro, bassist Furio Di Castri and, later, bassist Enzo Pietropaoli, keyboardist Danilo Rea and drummer Alberto D'Anna. Lingomania recorded three studio albums in the 1980s - Riverberi (1986), Grr...Expanders (1988) and Camminando (1989), all on Gala Records - and was voted best Italian group in Musica Jazz's critics' Top Jazz poll in 1984, 1985 and 1987. The band reunited in 2017 for Lingosphere (Abeat Records), with trumpeter Giovanni Falzone joining the original rhythm section of Fiorentino, Giammarco, Di Castri and Gatto.

While working within that circle, Fiorentino was a session guitarist on Gatto's Notes (1986/87, Gala Records), an album that also features the American tenor saxophonist Michael Brecker alongside Danilo Rea, pianist Rita Marcotulli, bassists Di Castri, Pietropaoli and Francesco Puglisi, Giammarco, trombonist Danilo Terenzi, Boltro and vocalist GeGè Telesforo. He also played guitar synthesizer on Paolo Damiani's Voices - Live in Rome (1989), alongside drummer Aldo Romano, and appears on Damiani's Unisoni from the same period.

Fiorentino released his first solo album, Inside Colors, in 1988 on Gala Records, built around a trio with Pietropaoli and Gatto and rounded out by bassist Luca Pirozzi, keyboardist Stefano Sastro and saxophonist Stefano D'Anna. Ulisse followed in 1995 on Caligola, a larger-ensemble session crediting bassist Dario Deidda, drummer Fabrizio Sferra, clarinetist Gabriele Mirabassi and tenor saxophonist Daniele Scannapieco; the album's own cover additionally bills American drummer Vinnie Colaiuta as a guest on three extra tracks, a credit sourced to the release itself and the artist's own biography rather than independently itemized in Discogs. Things to Come (2002, named in his biography but not found in Discogs) and Alice (2003, Brave Art Records, a solo-overdub record) rounded out his solo output of the period.

In 1998 he was also a guest guitarist on Grandi Spazi, the debut album by drummer Davide Pettirossi, and in 2006 played on pianist Carlo Mezzanotte's La Linea alongside Giammarco and Deidda.

From 2007 onward, Fiorentino's leader catalog shifted toward two long-running guitar-duo partnerships. The first, with Fabio Zeppetella, produced Temi, Variazioni e Metamorfosi (2007, Picanto Records) and Wordless Song (2019, Emme Record Label). The second, with Claudio Quartarone, began with Anamorfosi (2022, Birdbox Records), recorded in a single day at Nightingale Studios in a session dated November 2019, and continued with II (2024, also Birdbox). In 2017 he also wrote the Italian liner notes for guitarist Maurizio Brunod and Lorenzo Cominoli's duo album Kintsugi.

Outside jazz, Fiorentino spent several years as a touring and recording guitarist for the pop singer Mina, playing on three of her PDU-label albums: Cremona (1996), Leggera (1997) and Mina Celentano (1998, a duet album with Adriano Celentano).

Fiorentino's own biography and that of Rome's Saint Louis College of Music, where he has taught, also name a long list of live concert collaborations that have not been matched to a specific Discogs recording: Paolo Fresu, Palle Danielsson, Enrico Rava, Mike Stern, Vinnie Colaiuta, Albert Mangelsdorff, Bruno Tommaso, Ares Tavolazzi and others. These are reported here as named, press- and biography-sourced concert credits rather than verified recording sessions.

Teaching has run alongside performing for most of Fiorentino's career. He was a founding member of Percentomusica, a Rome music-education organization, and served two terms as its president. He has held jazz guitar faculty positions at the L. Refice Conservatory in Frosinone (2008-2012), the Cherubini Conservatory in Florence (2011-2016) and, since 2017, as full professor of jazz guitar at the Respighi Conservatory in Latina. He has also taught at Rome's Saint Louis College of Music, first from 1984 to 1988 and again since 2009. He has published two instructional books, Scale! (1999) and La Chitarra Jazz (2001), both with Carisch, and three instructional videos. He has repeatedly been voted best Italian jazz guitarist in the reader polls of the Italian magazines Chitarre and Guitar Club.

Fiorentino describes his own approach as a "less is more" aesthetic drawn from Jim Hall, whose 1969 album It's Nice to Be with You he has named as his single strongest influence: "Everything Jim played has a poetic and profound meaning... without frills of any kind." His earlier formation ran through fusion: John McLaughlin and the Mahavishnu Orchestra's Birds of Fire was, in his words, "a revelation" that arrived while he was listening to Genesis, King Crimson and Led Zeppelin, and pointed him back toward Miles Davis and John Coltrane. Pat Martino's Footprints then introduced him to post-bop phrasing. In more recent years he has pointed to Kurt Rosenwinkel, particularly the albums Reflections and The Next Step, as the guitarist he returns to most. He plays a Tele Thinline built by luthier Stefan Schottmueller and a Moffa Maestro archtop, the latter his guitar of choice in duo settings with Quartarone and Zeppetella, through a Fender Hot Rod Deluxe 40 George Benson amplifier.

Critics have made similar points about his playing across four decades: writing in La Repubblica, Ernesto Assante called him "without doubt one of the best Italian jazz soloists" with "few rivals" at the European level, citing his sustained work applying electronics to jazz guitar; Musica Jazz's Giuseppe Piacentino described a "substantial" musician whose technical command carries real sensitivity underneath it.