Aaron Cassidy (b. Illinois, USA, 1976) is a composer and conductor with a growing international presence. His work has been performed by some of the world’s premier contemporary music specialists, including ELISION, Ensemble SurPlus, Ictus Ensemble, ensemble recherche, 175 East, the Kairos, Diotima, and JACK string quartets, and soloists including Mieko Kanno, Garth Knox, Ian Pace, Christopher Redgate, and Carl Rosman, at festivals including Gaudeamus (Jurors Prize nominee, 2002 & 2004), Huddersfield, Warsaw Autumn, Bludenz, Samtida Musik Stockholm, June In Buffalo, and the ISCM World Music Days, and has been broadcast by the BBC, Radio France, Deutschland Radio Berlin, Österreichischer Rundfunk, and Polish National Radio. In July 2008, ELISION presented a portrait concert of his work in Brisbane for broadcast on ABC Classic FM, and in 2009-10 the ensemble has embarked on an extensive recording project of his work in conjunction with Radio Bremen. He has received grants, stipends, and commissions from allerArt Bludenz, the Yvar Mikhashoff Trust for New Music, Haupstadtkulturfonds Berlin, New York Foundation for the Arts, Schloss Solitude Sommerakademie, ASCAP, the American Music Center, the Arts and Humanities Research Council (UK), and Südwestrundfunk/ Donaueschinger Musiktage.

Also active as a conductor, Cassidy has led performances by student and professional ensembles in a diverse range of contemporary repertoire. He has conducted at the June in Buffalo festival and in a wide variety of university settings, currently serving as conductor of the New Music Ensemble and the Symphony Orchestra at the University of Huddersfield. In 2009, he participated in the Herrenhaus Edenkoben Mastercourse with Peter Eötvös and Zsolt Nagy, conducting the International Ensemble Modern Academy in a radio broadcast for SWR-2.

As an author his contributions include chapters in the first, second, and sixth volumes of Wolke Verlag's New Music and Aesthetics in the 21st Century series. Additionally, he has been increasingly active as a CD producer, most notably with EXAUDI Vocal Ensemble's critically-acclaimed recent releases on the NMC label and ELISION's recent Ferneyhough disc on Kairos.

In 2003, he completed a Ph.D. in Composition as a Presidential Fellowship recipient at the University at Buffalo (SUNY) under the guidance of David Felder, where he was awarded a Dissertation Fellowship for advanced research. He has studied additionally in masterclass and lesson settings with such composers as Richard Barrett, Chaya Czernowin, Brian Ferneyhough, Jonathan Harvey, Alvin Lucier, and Tristan Murail, among numerous others.

Cassidy joined the faculty of the University of Huddersfield as Senior Lecturer in Composition in the autumn of 2007 and serves as Coordinator of the MA in New Music at the university's Centre for Research in New Music. He previously served as Lecturer of Composition and Co-Director of New Music Northwestern at Northwestern University in Evanston, Illinois, and as Visiting Assistant Professor of Music at Buffalo State College.