Gianni Mimmo was born in Pavia, in Lombardy, on 13 February 1957, and is a soprano saxophonist, improviser, composer and record-label owner who is based in his home city. He is self-taught. In a 2007 interview with All About Jazz Italy he said he began playing the saxophone at fourteen, that the first jazz record he ever heard was Archie Shepp's Kwanza, and that he taught himself by following the forms of free jazz, starting on tenor and then spending years on alto and baritone. He recalled seeing the Art Ensemble of Chicago many times in its early years, including a Paris concert by a Roscoe Mitchell sextet. The turn to soprano came after the first Steve Lacy concert he attended, in Pavia, where Lacy played with the Bologna poet Adriano Spatola; he began writing to Lacy afterwards and later described what he took from him as an attitude toward music rather than a saxophone method. His own website describes him and his duo partner Harri Sjöström as pupils of Lacy. His All About Jazz biography adds that he works in a wind-instrument repair workshop in Pavia, which lets him make music without market pressure.

His early work was interdisciplinary. He began playing solo soprano concerts in 2000, started a long collaboration with the poet Chandra Livia Candiani the same year (the performance Lettere mai scritte), and in 2002 founded the duo Bespoken with the sampling artist Lorenzo Dal Ri. A 2004 duo with the trombonist Angelo Contini produced Two's Days / Tuesdays, and in 2005 he, Contini and the guitarist Xabier Iriondo recorded the music for Kursk _ Truth In The End, an audiovisual piece about the Russian submarine disaster of 2000 with a film by Agua Mimmo and photographs by Elda Papa.

In 2006 he launched Amirani Records with his solo album One Way Ticket (AMRN001), followed the same year by the Contini duo and Bespoken. All About Jazz Italy profiled the new label in March 2007 as a "double surprise" from an almost unknown soprano player. Amirani grew into one of the main independent outlets for improvised and contemporary music in Italy: its catalogue reached number AMRN075 in 2023, and All About Jazz's April 2021 interview with him put the catalogue at sixty-five titles, and he said there that he insists each release be rigorous enough to deserve a place in a catalogue. He has produced records for other artists as well as himself, among them the pianists Gianni Lenoci and Nicola Guazzaloca, a 2008 Brussels quartet record by Anthony Braxton with Cristiano Calcagnile and Antonio Borghini, and a tribute to Julius Hemphill.

As a player he works mostly in duos and trios. A Watched Pot (Never Boils) (2007) paired him with cellist Andrea Serrapiglio and drummer Francesco Cusa; Your Very Eyes (2008) with Iriondo was recorded at dawn on the summer solstice in a 10th-century cave-church in Matera. The Shoreditch Trio with pianist Nicola Guazzaloca and cellist Hannah Marshall recorded in London and Brussels (2010-2011), and a piano duo with Gianni Lenoci, Reciprocal Uncles, ran from 2009 until Lenoci's death; Township Nocturne (2021) with Cusa and bassist Pierpaolo Martino was recorded a year and a day after that death, in his memory. A duo with the New York cellist Daniel Levin produced Turbulent Flow (2012) and shows at New York's Vision Festival and in Brooklyn; the violinist Alison Blunt has been a duo partner since 2013 (Lasting Ephemerals, 2014; Busy Butterflies, 2019), with more than sixty concerts including a three-week United States tour and an appearance at the Society for Improvised Music conference in New York in 2015. With Sjöström he made Live At Bauchhund Berlin 2010 (2011) and Wells (2023), and co-led the six-piece Sestetto Internazionale on a 2015 tour of Finland and Germany.

He also writes for larger forces. Prossime Trascendenze (2016) sets graphic scores for a quintet and a sextet, with Blunt, violist Benedict Taylor, trombonist Angelo Contini and others, and the wind quartet piece Amphidromic Cotidal (2013) is built from observation of tide cycles. He has scored live soundtracks for Lotte Reiniger's silent film The Adventures of Prince Achmed (Bergamo Film Meeting, with Bergamo Jazz, 2016) and, with Iriondo and Calcagnile, for Sergei Parajanov's Sayat Nova (released as Mantic, 2012).

In 2018 three records appeared in quick succession: Clairvoyance, the first album by his trio with pianist Silvia Corda and double bassist Adriano Orrù; Explicit, a duo with the Los Angeles reed player Vinny Golia; and Triad, recorded in Milan with pianist Satoko Fujii and bassist Joe Fonda after Long Song Records' Fabrizio Perissinotto arranged the session for Fujii and Fonda's 2017 Italian visit. Clairvoyance made Transient (2022) and, in 2026, Chapters of a Day, drawn from a February 2025 concert at the Auditorium Fondazione Piacenza-Vigevano. That live album is the third release on Rosebud Relevant Records, the label he started in 2025 as what he called a personal journal of the pages that matter in his path; its first two are the solo record The Lonesome Thing (2025) and the duo Blowing on the Knots (2026) with the vocalist Viv Corringham.

His work has been reviewed by All About Jazz (largely by Neri Pollastri and Mark Corroto), Avant Music News, Percorsi Musicali and Touching Extremes, among others. All About Jazz Italy named Live At Bauchhund Berlin 2010 a "must have" album, per his own site, and Pollastri's 2024 live review called Clairvoyance one of the most interesting groups active in Italy.

Mimmo plays only soprano, an instrument that, as he explained in the 2007 interview according to Pollastri, he chose for its imperfection: it demands close attention to sound and so opens more timbral possibilities than its siblings. His stated influences are Steve Lacy and Roscoe Mitchell in jazz, John Cage, Earle Brown and Robert Ashley among contemporary composers, and painters including Jackson Pollock, Toti Scialoja, Piet Mondrian, Mario Sironi and Felice Casorati, several of whom are named in album dedications and in the compositions of Prossime Trascendenze, Further Considerations and the solo work 7 Paintings. His own website describes his music as focused on the treatment of timbre and advanced technique on the soprano, and on the relationship between a single melodic line and silence; the avant-garde critic Daniel Barbiero, quoted there, writes that it rests on a balance of abstraction and direct lyricism.

Most of his records are free improvisation in small chamber-like combinations, often with cello, violin, piano or reeds rather than a rhythm section, though he also writes graphic scores and text-based pieces and works with poets, dancers and film-makers. All About Jazz's Mark Corroto described his tone on Flawless Dust (2016, with guitarist Garrison Fewell) as luscious even when extended techniques are used. Mimmo has said he is drawn to encounters with contemporary classical music, post-rock and other areas outside jazz, and that he finds some of his most useful contacts outside it.