Daniele D'Agaro was born August 13, 1958, in Spilimbergo, in Italy's Friuli region. He took up saxophone at sixteen, and by 1979 was already working outside Italy, alongside fellow Friulian free-jazz pioneer Andrea Centazzo's Mitteleuropa Orchestra, before moving that year to Berlin, where he studied with Heinz von Hermann of the RIAS Berlin Radio-Television Orchestra. In 1983 he relocated again, first to Eindhoven and then to Amsterdam, enrolling in the jazz department of the Sweelinck Conservatorium.

Amsterdam placed him inside the city's improvised-music scene for more than a decade. He co-founded the trio Lingua Franca with cellist Tristan Honsinger and bassist Ernst Glerum, recording their self-titled album for the American free-jazz label Nimbus West on June 28, 1989. He also worked inside South African-Dutch saxophonist Sean Bergin's group M.O.B., and from the early 1990s formed Trio San Francisco with Bergin and fellow reedist Tobias Delius, a group built around blending free improvisation with South African kwela music. Alongside these smaller units he became a member of pianist Alexander von Schlippenbach's Globe Unity Orchestra, the pan-European free-jazz big band founded in 1966 - a standing group affiliation documented on Discogs and marked, in 2018, by his appearance on the retrospective release Globe Unity - 50 Years.

D'Agaro returned to live in Udine in 1996, without ending the international partnerships built in the Netherlands. Drummer Han Bennink went on to record three separate trio or quartet albums with him over the following decade - Strandjutters (2003, hatOLOGY, with bassist Ernst Glerum), The Tempest (2008, Artesuono, with organist Bruno Marini) and Fingerprints (2010, Artesuono, again with pianist Alexander von Schlippenbach) - and Schlippenbach himself had already recorded the duo album Dedalus (2007, Artesuono) with him. In 2005 D'Agaro founded his own big band, the Daniele D'Agaro Adriatics Orchestra, which set Friulian and Balkan folk material and African percussion inside free-jazz horn writing; its three albums - Comeglians (2007), Exotica Domestica (2009) and Mountains, Love & Humour (2012, with a personnel that included Bennink, Tobias Delius, Sean Bergin, trombonist Wolter Wierbos, organist Bruno Marini and, on double bass, Alessandro Turchet) - were issued on El Gallo Rojo and Artesuono. In 2006 he founded and became artistic director of the festival I Suoni della Montagna. Musica Jazz's Top Jazz critics' poll named him Italy's best saxophonist and clarinetist in both 2007 and 2008, and in 2010 he placed first in the Jazzit Awards individually while the Adriatics Orchestra placed first in that year's orchestra category.

D'Agaro's American connections run through Chicago specifically: Chicago Overtones (2005, hatOLOGY) paired him with trombonist Jeb Bishop, bassist Kent Kessler and drummer Robert Barry - Barry a founding member of Chicago's Association for the Advancement of Creative Musicians - and he has performed at both the Chicago Jazz Festival and the North Sea Jazz Festival in the Netherlands. In 2016 he recorded a duo album with the Japanese-German avant-garde pianist Aki Takase for Artesuono, released jointly under both names. His catalog since has continued to mix small-group settings - the Giovanni Maier/Zlatko Kaučič trio Disorder at the Border (2014, with a 2021 live sequel and a 2022 expansion, Kataklisma, adding Tobias Delius), the reed-and-flute trio Tea Time with Massimo De Mattia and Maier (2016) - with a 2022 duo tribute to Charles Mingus, Mingus Fingers (Artesuono), recorded with fellow Friulian double bassist Alessandro Turchet; the two had already played together as sidemen in the Maurizio Pagnutti Sextet on Secret Stories (2010, Artesuono) and in the Adriatics Orchestra's Mountains, Love & Humour two years later.

D'Agaro's Discogs-documented ties to saxophonist Cristina Mazza run to two separate sessions eight years apart. In 2008 both are credited as performers and co-writers on American drummer Jimmy Carl Black's Freedom Jazz Dance (Azzurra Music), alongside baritone saxophonist Bruno Marini. Then, in February 2007 (recorded before the Black session was released, but issued after it), D'Agaro joined a Verona sextet Mazza organized to record the music of pianist Mal Waldron, alongside Sean Bergin, Marini, Jean-Jacques Avenel and Sangoma Everett; the results sat unreleased for fourteen years before Caligola issued them as Celebrating the Music of Mal Waldron in 2021, with D'Agaro taking the tenor saxophone solo on the title suite, a credit independently confirmed at the Discogs release level. Teaching has run alongside his performing career: in January 2025 he led a masterclass on ensemble music applied to jazz history at the Conservatorio "Tartini" in Trieste, under the supervision of bassist Giovanni Maier, one of his own recurring duo and trio partners.

D'Agaro's tenor saxophone and clarinet voice sits inside the Dutch/German free-improvisation lineage he absorbed directly during his Amsterdam years - the same circle that produced Han Bennink, Alexander von Schlippenbach and the Globe Unity Orchestra - built around a wide-vibrato tone and a range running from gentle melodic phrasing to extended overblowing. That free-jazz core sits alongside two other identifiable threads in his catalog: an ethnographic, folk-inflected big-band voice through the Adriatics Orchestra, which set Friulian and Balkan material and African percussion inside jazz horn arrangements, and a string of tightly-focused duo records - with Schlippenbach, with Aki Takase, with Alessandro Turchet - that strip his sound down to a single conversational partner at a time.