Gabriel Marciano was born on August 10, 1998, in Cava de' Tirreni, in the province of Salerno. A festival biography says he took up the saxophone as a child, at about ten, with a strong pull toward jazz that his parents had passed down. He began with Antonio Giordano, a saxophonist from the Salerno area, and continued at the Liceo Musicale Alfano I in Salerno with Giuseppe Esposito. He later earned both a first-level and a second-level diploma in jazz saxophone at Rome's Conservatorio Santa Cecilia, and he teaches saxophone, jazz improvisation, harmony and ear training at Rome's NEXT Music Academy.

His summer-seminar record started early. In 2015 he was named best saxophone student at the Nuoro Jazz seminars. In 2016 he took part in the Berklee at Umbria Jazz Clinics, winning a $20,000 scholarship toward Berklee's bachelor program, along with a best-student honor that put him on stage at Umbria Jazz Winter that year. Italian Wikipedia's page for the Berklee Umbria Jazz Award lists his name among the award's winning musicians. He also attended advanced masterclasses at Siena Jazz, Nuoro Jazz, Tuscia in Jazz and Jazz in Laurino. In 2018 he was selected by The New School for Jazz and Contemporary Music in New York City for its bachelor program, and Cava de' Tirreni's daily paper Il Portico reported the news that May, calling him at twenty already a reference point for jazz in Italy.

The biography circulated with his festival listings says the New York years brought him into contact with Joe Lovano, Peter Bernstein, Miguel Zenon, Will Vinson, Aaron Parks, Dayna Stephens, Ben Wendel, Joe Sanders, Immanuel Wilkins, Kurt Rosenwinkel and Ferenc Nemeth. The wording is about contact and study rather than recording credits.

Back in Italy he settled in Rome and formed the Gabriel Marciano Quartet with pianist Vittorio Esposito, double bassist Alessandro Bintzios and drummer Cesare Mangiocavallo. Sources date the group's start anywhere from 2019 to 2021; by 2026 Casa del Jazz was describing more than five years of concerts across Italy and Europe and more than 50 performances. The quartet has played Casa del Jazz and the Auditorium Parco della Musica in Rome, the San Teodoro Jazz festival in Sardinia (September 3, 2023), the Gaeta Jazz Festival, Urbino Plays Jazz, the Nuoro Jazz Festival, Baronissi Jazz Summer, the Italian Jazz Trilogy series in Skopje, JazzMi in Milan, and clubs in Madrid (Club Matador), Malaga (Clarence Jazz Club) and Dortmund (Bunt oder Blau). Marciano has also appeared at the Sibiu Jazz Festival in Romania and the Caracalla Music Festival in Rome.

The quartet's debut, A Reason To Believe, was recorded in May 2023 at the studios of the Auditorium Parco della Musica "Ennio Morricone" in Rome and released on November 29, 2024, by Parco della Musica Records, produced by Fondazione Musica per Roma. All of the music is by Marciano, and he describes it as an account of the previous ten years of his life, covering places, people and the ambitions he has carried since childhood. The nine tracks run from the opener "Heroes" and "Signs of Them" through the title piece, "Emerald Meteors" and "Annie's Place" to a closing live improvisation. Casa del Jazz's 2026 concert listing for the group carries the tag "Young Lions."

Outside his own quartet, Marciano is the alto saxophonist of Wasted Generation, a Rome quintet with trumpeter Iacopo Teolis, pianist Vittorio Solimene, double bassist Giulio Scianatico and Mangiocavallo on drums. Their debut, Introducing Wasted Generation (GleAM Records, 2023), was produced by American bassist Joe Sanders and reviewed by All About Jazz, which described a young band focused on free contemporary jazz, melodic exploration and an avant-garde approach to improvisation. Marciano wrote the opening track, "Omron," and is credited on the Discogs entry as alto saxophonist. In 2026 he also played alto saxophone on singer Sonia Ziccardi's debut album Driade (A.MA Records, released March 13, 2026), alongside Solimene on piano, Bintzios on double bass and Federico Chiarofonte on drums. All About Jazz singled out his lines on the opener "Capital Sins."

His 2026 activity shows the range of his work. On March 22, his quartet opened the bill at the Festival Jazz Idea in the Sala Accademica of Santa Cecilia, ahead of the duo of French clarinetist Louis Sclavis and double bassist Daniele Roccato. On July 9, the Federico Campanello Quartet, in which Marciano plays alto saxophone alongside trumpeter Niccolò Monterizzi, bassist Federico Campanello and drummer Elisabetta Saviano, won the 2026 Conad Jazz Contest run by Umbria Jazz. The prize is EUR 5,000, a tour that includes Jazz Italiano per L'Aquila (September 5 to 6, 2026) and Umbria Jazz Winter in Orvieto (December 30, 2026 to January 3, 2027), and distribution of an EP through Universal Music Italia. Earlier, in 2021, he was credited as a featured player on the single collection Pietralata Session, Vol. 1 by Re Mida, Francesco Fratini, Giuseppe Romagnoli and Matteo Bultrini.

The quartet's own listings place its music in the modern New York jazz tradition: a repertoire of Marciano originals with strong New York influences, some American standards interpreted in a personal way, and elements of the traditional music he grew up with in Campania. A festival biography names Ambrose Akinmusire, Immanuel Wilkins, Walter Smith III, Kurt Rosenwinkel and Logan Richardson as reference points for his writing and improvising, alongside the masters of the jazz tradition. Wasted Generation, by contrast, leans toward free contemporary jazz, and the two settings together mark his range: composed, story-driven quartet music on his own record, and collectively written, open improvisation with peers.