Marcello Di Leonardo was born in Pescara in 1969, took a classical training and worked through a run of jazz summer seminars before moving to Rome in 1992, at twenty-three. The move gave him the introductions that set up everything after it. His own account names the clarinettist Tony Scott, the Roman altoist Massimo Urbani, Benny Golson and Jon Faddis among the players he worked with in those first Roman years, and Urbani died in June 1993, which puts that encounter inside a narrow window. A period of steady work in Spain and Portugal followed, where he played and recorded with Rick Margitza, Phil Markowitz, Bill Pierce, Ed Neumeister and Steve Slagle. Two records survive from it: pianist Carlo Morena's The Next Music (Movieplay, 1996), a quartet with Margitza on saxophone and Bernardo Moreira on bass, and Moreira's own Tudo Muda (Movieplay, 1998) with Slagle. His earliest credit of all is on accordionist Oberdan Fratini's Apres Midi (Raptime, 1990), before the Rome move; his first substantial Italian date was saxophonist Francesco Santucci's Who's Seen Katty Page?, cut at G.C. Studio in Rome in June 1992 and issued by Penta Flowers in 1993.

Two partnerships formed in the mid-1990s and both are still running. In 1996 he joined Maria Pia De Vito's quartet with Enzo Pietropaoli on bass and Danilo Rea on piano, with Rita Marcotulli taking the piano chair the following year. He is on Fore Paese, recorded at Studio Il Parco in Naples in January 1996 with Paolo Fresu guesting on two tracks, and on Triboh (1998), the trio record De Vito made with Marcotulli and the Armenian percussionist Arto Tuncboyaciyan. At the same moment he became the drummer in guitarist and composer Battista Lena's orbit, which is where the most unusual music of his career sits. Banda Sonora (Label Bleu, 1997) was taped on November 30 and December 1, 1996 at the Teatro Poliziano in Montepulciano, setting a jazz quintet with Enrico Rava and clarinettist Gabriele Mirabassi against the full sixty-piece town band of Chianciano Terme. Mille Corde (Egea, 1999) added Fresu and the accordionist Gianni Coscia. I Cosmonauti Russi (Label Bleu, 2002) was recorded across Chianciano Terme, Siena, Rome and Amiens between June 2001 and January 2002 with an even larger clarinet and trumpet section. The group took that repertoire to Umbria Jazz in 1997 and to the Théâtre de l'Odéon in Paris and the Beijing and Shanghai jazz festivals in 1998.

Lena also brought him into Italian film. Di Leonardo drums on Lena's scores for Paolo Virzì's Ovosodo (1997) and on five films by Francesca Archibugi, running from L'albero delle pere (1998) and Domani (2001) through Questione di cuore (2008), Gli sdraiati (2017) and the television series Romanzo familiare (2018). He later worked on two 2019 features scored by Maurizio Filardo, Brave ragazze and Domani è un altro giorno, and on Giorgio Tirabassi's Il grande salto, again with Lena writing.

In 2000 he took the drum chair in Enrico Pieranunzi's trio, which is the most exposed straight-ahead work in his catalogue. Multiple Choice, cut in Zurich on March 20, 2000 with Piero Leveratto on bass, is a trio record with almost nothing to hide behind. Evans Remembered, recorded at Millesuoni Studio in Rome on October 11 and 12, 2000, expands the group with Fabrizio Bosso, Rosario Giuliani and Mirabassi. Pieranunzi also used him on the Sgt. Pepper e Mr. Miles project at Roccella Jonica in 2000 and, in the Fellini Jazz band, gave him the hardest single assignment of his career: standing in for Paul Motian on a tour with the Belgian trumpeter Bert Joris, Tony Malaby on saxophone and Marc Johnson on bass, which reached the Auditorium Parco della Musica in Rome on October 30, 2003. In 2001 he played the Jazz'n Fall series in Pescara opposite three generations of guitarists, Mundell Lowe, John Pisano and Philip Catherine.

Giuliani's Dreyfus Jazz contract turned his quartet into a touring proposition and Di Leonardo held the drum chair through it. Mr. Dodo (Dreyfus, 2002), with Pietro Lussu on piano and Dario Rosciglione on bass, is the studio document; the itinerary took in Jazz à Vienne, the JVC Jazz Festival, Jazz in Marciac, Jazz des Cinq Continents, the North Sea Jazz Festival, the London Jazz Festival, the Ankara Jazz Festival and a run at Smoke in New York for the Italian Jazz in New York series, with Joe Locke, Catherine and Bob Mintzer sitting in on occasion, including at Jazz & Image in Rome in 2002. Bosso's own Fast Flight (Red Records, 2000) is from the same circle. Alongside it he worked the commercial end of Roman music: three years from 2004 on Paolo Bonolis's RAI programme Il senso della vita in Stefano Di Battista's house band, two musicals with the actor Alessandro Preziosi, four albums with the singer Nicky Nicolai for Virgin, EMI and Sony, a date with Adriano Celentano, and a night with Ivan Lins at Umbria Jazz in 2004.

By 2009 he was the drummer a Roman producer called when a record needed a rhythm section, which is how he came to play on tracks 3 to 6 of Yakir Portrait (Philology, 2009), the debut of the blind Israeli pianist Yakir Arbib, paired there with Pietropaoli against two other rotating rhythm sections. The decade after it produced his most settled band: pianist Claudio Filippini's trio with Luca Bulgarelli on bass, which made three albums for CAM Jazz, The Enchanted Garden (2011), Squaring the Circle (2015) and Before the Wind (2018), and played the Italian Cultural Institute in Tokyo and the Delhi Jazz Festival in 2016. In 2013 he formed The Golden Circle with Giuliani, Bosso and Pietropaoli, a co-billed quartet built on Ornette Coleman's 1965 Stockholm records and recorded at Oneemusic Studios in Rome that March; Di Leonardo contributed the original "Caffeine" to it, and the band played the Qatar Jazz Festival and Umbria Jazz in 2016. From 2013 he has also been the drummer in Eduardo De Crescenzo's Essenze Jazz, the songwriter's jazz-quartet reworking of his own catalogue.

His first record under his own name arrived in 2023, thirty-one years after the move to Rome. The Magic Box (Jando Music / Via Veneto Jazz) is eight Di Leonardo originals written toward the jazz film scores of the 1960s and 1970s, recorded in the Casa del Jazz studios in Rome with Rick Margitza on tenor, Julian Oliver Mazzariello on piano and Rosciglione on bass. It was launched at the Casa del Jazz on November 24, 2023 and the band took it to Pescara Jazz, his home festival, in July 2024. The following year brought We Concentrate On You, a Cole Porter programme cut for the audiophile label Fonè and billed, pointedly, to the Leaderless Quartet: Mirabassi on clarinet, Fulvio Sigurtà on trumpet, Pietropaoli and Di Leonardo. He has taught jazz drums at the conservatories of Pescara, Mantova, Fermo, Teramo, Bologna, Latina and Avellino, and wrote Crossed Times, a book of rhythmic independence exercises whose premise is that the coordination work can be done by hitting your knees and the floor, with no drum kit involved.

Di Leonardo is a supporting drummer by temperament and the shape of his catalogue proves it: roughly fifty-five recordings across thirty-five years, almost all of them somebody else's, and a first leader date at fifty-four. The work divides cleanly in two. In the piano trios, Pieranunzi's and later Filippini's, he plays close and quiet, with brushes and cymbal detail carrying the time and very little of the kit in use at any moment, which is why those records give him so much room. In Battista Lena's projects he does something few jazz drummers are asked to do at all, holding a jazz pulse underneath a sixty-piece Italian town band on Banda Sonora without either flattening the band or being swallowed by it. The Golden Circle is the exception in both directions: on Ornette Coleman's material, and without a chordal instrument in the quartet, he plays loosely and conversationally in the Ed Blackwell manner the repertoire asks for. As a writer he came late and came narrow. The eight originals on The Magic Box are deliberately cinematic, built on the vocabulary of Italian and American film jazz of the 1960s, and the record's cover puts a cajón and a pair of brushes where a portrait would normally go, which is about as accurate a self-description as a sideman of his kind is likely to offer.