Roberto Manzin was born on July 8, 1966, in Rome to Eastern European refugee parents who were themselves musicians. The family moved to Milan when he was five, and he trained there privately and at the Civica Scuola di Musica Villa Simonetta. Through the 1980s he worked the Milan club circuit, playing rooms including Il Capolinea and Le Scimmie and touring with Italian singer-songwriter Enzo Jannacci. In the 1990s he became a member of the Tony Scott Jazz Quintet, led by the American bebop clarinetist who had recorded with Charlie Parker and Billie Holiday and settled in Italy in the 1970s, and he built a parallel career as one of Milan's busiest studio saxophonists, recording with a wide range of Italian pop and Latin artists and appearing on television commercials; by his own account and AllAboutJazz's biography of him, he contributed to eight albums in 1992 alone. One of his own leader credits from this period, the 1991 compilation Sax Project (Duck Record), is an easy-listening saxophone-covers record of pop standards such as "Feelings" and "What a Wonderful World," reflecting the commercial side of that era's work rather than a jazz date.

Manzin relocated to London in the late 1990s and has been based in the UK since, with a spell in Berlin in the early 2020s before returning to Britain; he now lives in Southend. His session and sideman credits in this period span genres widely, including guest and track appearances on records by Spanish singer Alejandra Guzmán, Spanish pop star Alejandro Sanz, soul vocalist Mario Biondi, guitarist Antonio Forcione, and singer-songwriters Rumer and Laura Mvula, and he has performed and recorded with Martha Reeves and the Vandellas, Donna Summer, drummer Dave Weckl, and James Brown in studio and television settings.

Alongside this session work, Manzin has built a sustained identity as a working jazz saxophonist and bandleader. He was a member of English pianist Dan Banks's working quintet, appearing on its two studio albums, Two in a Box (2017) and Simulated Cities (2018), both Discogs-tagged Jazz with Post-Bop, Contemporary Jazz, and Modal styles. In 2020 he formed Redbeetroots, a Berlin-based quartet with pianist Davide Incorvaia, electric bassist Francesco Beccaro, and drummer David Guy, releasing the album Blue Feather (2021), built entirely from his own compositions. He also leads his own Roberto Manzin Quartet in London, with pianist Will Butterworth, bassist Marcus Penrose, and drummer Keith Michael, and performs regularly on the UK jazz-club circuit, including residencies and guest appearances at Ronnie Scott's, the PizzaExpress Jazz Club, Hampstead Jazz Club, and the touring Jazz 825 concert series. In late 2023 he appeared as tenor saxophonist on pianist Terence Collie's quartet album 384,400, reviewed in The Jazz Mann as featuring "the impressive Manzin" across several tracks.

Manzin's catalog splits along a genuine line between commercial session work and a sustained jazz identity, and both sides are real. His only leader credit from his Italian period, Sax Project (1991), is a smooth, covers-based easy-listening saxophone record rather than a jazz date, and the bulk of his documented 1990s session discography is pop, Latin, and TV-commercial work for other artists rather than his own jazz output. Set against that, his working bands since the mid-2010s, Dan Banks's quintet, his own Redbeetroots, and the Roberto Manzin Quartet, are consistently Discogs- and press-classified as jazz (Post-Bop, Contemporary Jazz, and Modal tags on the Dan Banks Quintet albums; Redbeetroots is described by its Berlin presenting venue as blending modern jazz and fusion with contemporary and world-music nuances). He has a real credential from the bebop tradition through his 1990s tenure in the Tony Scott Jazz Quintet, led by a clarinetist who played with Charlie Parker and Billie Holiday, and he has been reviewed as a jazz soloist by name in dedicated UK jazz press: The Jazz Mann praised his tenor playing on 384,400 as "stretch[ing] out expansively and effectively" and compared a solo on that record to "his punchy playing as a guest with guitarist Clement Regert's Wild Card trio," while Time Out called him a "scorching tenorist" and likened him to Michael Brecker and Jerry Bergonzi. He maintains a listing as a working musician on All About Jazz and plays the UK's dedicated jazz-club circuit as a leader in his own right, not only as a hired sideman.