Gianni Giudici is a Milan-born Hammond organist whose career runs on two tracks that rarely overlap in one person: he has been a working jazz organ player since his teens, and for 35 years he was one of the people designing the electronic keyboards other musicians play. His own biography says he began on the Hammond at fifteen and became the company's official demonstrator and concert artist in Italy at seventeen, a post he held from 1970 to 1974, and he describes himself as the youngest such demonstrator in Europe. In an interview with the magazine Strumenti Musicali he named the American Hammond players Shay Torrent, Axel Alexander, Bryan Rodwell, Jerry Allen and Champ Champagne as the artists he learned from in those years. In June 2007 the International Archive of Jazz Organ in Cologne named him its Organist of the Month, and in June 2011 Strumenti Musicali put him on its cover as "The Hammond Padrino."

His first organ trio, formed at seventeen or eighteen depending on the source, was with drummer Tullio De Piscopo and guitarist Bruno De Filippi. He co-founded a blues band with Cooper Terry and Larry Nocella, played in Johnny Sax's band as the successor to keyboardist Dario Baldan Bembo, and spent three years on the Milan jazz circuit in clubs including the Capolinea, the Club 2 di Brera and the 17 Jazz Club. He also recorded on pop sessions for Adriano Celentano and Gino Paoli, and his website lists the credit on Celentano's Svalutation as ARP 2600 synthesizer rather than organ. At around twenty he was offered a tour with Mia Martini's band and turned it down for a job as a technical consultant, moving from Milan to the Marche region.

That job became his second career. In 1974 Matteo Galanti brought him into the technical team of Generalmusic, the Italian instrument maker, where he rose to musical director, head of research and development and vice president over more than three decades, working on the Hammond Concorde, the GEM Synthex and the company's arranger workstations. Since 2010 he has been brand manager and music director at Studiologic, the Fatar keyboard brand, whose tonewheel organ clones were developed with Joey DeFrancesco and Brian Auger, according to his conservatory biography. His compositions are published by Ricordi. He has taught master classes on the organ and electronic keyboards at the Conservatorio Rossini in Pesaro, including a workshop series in January and February 2022, and a 2014 Bergamo concert notice describes him as having adopted Romagna as his home.

The recordings that carry his name as a jazz musician are mostly live and small-group. On Terre Rare (Music Center, 2001), an album billed to guitarist Dario Faiella's q.tet, he plays organ next to pianist Stefano Bollani, bassist Riccardo Fioravanti, drummer Christian Meyer and saxophonist Michael Rosen, a credit confirmed on Discogs. Hot Interplay (Tuscia in Jazz, catalogue TIJ 0902) is the record billed to him: a live theater date with Max Ferri on drums, Alessandro Fariselli on saxophones and Fabrizio Bosso on trumpet and flugelhorn, dated 2008 on Discogs. The Jazz Convention review called it hot and engaging and singled out Bosso for adding color to the front line; the set includes Wayne Shorter's "Footprints" and Lou Donaldson's "Alligator Bogaloo." The same organ-and-saxophone-and-drums trio, billed as HOT trio, made Grab My Groove (RaRa Records, 2011), with trumpeter Flavio Boltro as special guest, a billing printed on the cover.

He is also a sideman across a wide stretch of Italian club and studio music. Discogs credits him on Fender Rhodes on "Close to My Heart" on Jestofunk's Seventy Miles from Philadelphia alongside American alto saxophonist Eric Marienthal, on Hammond organ on "Ecstasy" on Mario Biondi's If (Tattica, 2009), and on Hammond on the Paola Lorenzi and Pedro Mena Peraza album En La Imaginacion, a jazz tribute to the Cuban composer Marta Valdes recorded in Riccione in April 2015. His own website adds the Havona Jazz-Funk Band records Havona and Terminal 3 (RaRa Records), a guest spot with the Riccione Jazz Orchestra on East Coast Big Band and Renzo Arbore's Vintage!... Ma Non Li Dimostra. Italian sources list Al Grey, Eddie "Lockjaw" Davis, Bobby Watson, Benny Bailey, Tony Scott, Valery Ponomarev, Terry Gibbs, Chet Baker, Gary Burton, Milt Jackson and Ingrid Jensen among the musicians he has played or recorded with; those relationships come from his biographies and are not itemized in his Discogs credits.

Giudici plays the Hammond tonewheel organ, usually in an organ trio or an organ, saxophone and drums group with a guest horn. The repertoire on Hot Interplay leans on hard bop and soul-jazz staples, "Footprints" and "Alligator Bogaloo" among them, plus "Just Funk," and the HOT trio records carry the same groove-forward approach. The Studiologic tonewheel-organ clones he oversees as brand manager were developed with two organists from that lineage, Joey DeFrancesco and Brian Auger. The ARGO review of the Havona album Terminal 3 calls him one of Europe's finest jazz organists, a description that also appears in his own biography.