Marco Ratti was an Italian jazz double bassist whose five-decade career made him one of Milan's most consistently working sidemen in traditional and swing jazz. Born in Monopoli, in Puglia, on January 13, 1932, he moved to Milan with his family as a child. He began playing double bass there alongside his brothers Franco, a guitarist, and Giancarlo, a drummer, forming a trio inspired by Django Reinhardt.

In 1956 the three brothers, together with guitarist Ico Cerutti, became the backing band for a young rock and roll singer just starting out, Adriano Celentano, under the name I Rock Boys. Keyboardist Enzo Jannacci, arriving the following year from Tony Dallara's backing group, completed the lineup. The band played Milan's major venues of the period and appeared at the "Primo Festival del Rock and Roll," held at the Palazzo del Ghiaccio on May 18, 1957. Ratti continued playing jazz throughout this period, forming a quintet with his brothers called I 5 Bix. He also worked as a bassist behind singer Mina, appearing in a widely reproduced photograph playing double bass in Bruno De Filippi's orchestra during a performance of "Tintarella di Luna."

Ratti's Discogs-documented recording career runs from a 1962 session with Trio Cusumano through a 1993 swing date, and centers on Milan's traditional-jazz and dixieland circuit. He is Discogs-credited on double bass on Archetipo - Il Jazz Libero Europeo Di Enrico Intra (1969, Rifi), led by pianist and composer Enrico Intra. When American violinist Joe Venuti toured Italy in 1971, Ratti was his bassist for the engagement, playing alongside pianist Lou Stein and drummer Gil Cuppini; those sessions were issued as Violinology, The Incredible Joe Venuti, and, in the Curcio reissue series, I Giganti Del Jazz Vol. 23. Ratti also recorded and toured through the 1970s with guitarist and banjoist Lino Patruno, including the Milan sessions issued as Welcome Joe! (1974) with Venuti and Patruno, and the small-group date Big Four (1982, released together with Jazz For Two as a compilation with Oscar Klein), on which he is one of the four billed musicians alongside Patruno, Klein, and saxophonist Carlo Bagnoli. Through Patruno's Milan College Jazz Society, Ratti also backed touring American swing and dixieland musicians including Bud Freeman, Wingy Manone, Jimmy McPartland, Dick Cary, Billy Butterfield, and Eddie Miller on a series of Carosello label live recordings between 1975 and 1979.

Beyond the traditional-jazz circuit, Ratti worked as a Milan session bassist across popular and cantautore recordings of the 1960s and 1970s, including sessions for Gino Paoli and for the "Cantacronache"-adjacent political song scene (Ivan Della Mea, Giovanna Marini, Paolo Pietrangeli, Fausto Amodei), and he is credited on Franco Cerri's guitar date Back To Jazz (1986), which also credits pianists Dado Moroni and Renato Sellani, trumpeter Emilio Soana, and vibraphonist Paolo Conte. According to Italian Wikipedia, he worked for many years with the vocal-jazz group Mnogaja Leta Quartet, who released the album Good News (1987). His last Discogs-documented recording is Milan Swing (1993, L+R Records), a swing session led by saxophonist Paolo Tomelleri and clarinetist Fritz Hartschuh.

From October 1978, Ratti taught double bass at the Scuola Nuova Milano Musica in Milan. A serious car accident in 2003 halted his musical activity for more than a year. He died in Milan on May 27, 2007, survived by his wife and daughter, Raffaella.

Ratti's playing sat squarely in the swing and dixieland tradition that has run through Milan's jazz scene since the 1950s: a walking, time-keeping double bassist built for small combos and revivalist big bands rather than a soloist with a recorded book of his own. His formative influence, by his own group's name, was Django Reinhardt's Quintette du Hot Club de France, and his most visible recorded work came behind Joe Venuti and inside Lino Patruno's dixieland and Milan College Jazz Society ensembles, alongside American swing-era visitors such as Bud Freeman and Wingy Manone. His one clearly modern-jazz credit, on Enrico Intra's 1969 chamber-jazz album Archetipo, shows a working bassist moving between the traditional-jazz rooms that defined most of his career and Milan's more exploratory scene when the call came.