He has received awards from ASCAP, Meet the Composer, the American Music Center and New Dramatists. His Ben Jonson Songs won Grand Prize at the San Francisco Song Festival and he has been honored with Copland House and Millay Colony residencies as well as commissions from the Estate Project for Artists with AIDS, the Five Borough Music Festival and the Sorel Foundation. Notable presenters of his music include: Guggenheim Works and Process, American Opera Projects, Mirror Visions Ensemble, New York Festival of Song, Harvard Ballet Company, Dancers Responding to AIDS, SongFest and New York City Opera’s Vox Series. His opera, A Letter to East 11th Street (with a libretto by Mark Campbell) was the first winner of the Domenic J. Pellicciotti Opera Composition Prize in 2014 and received a full production with the Crane Opera Ensemble at the State University of New York in Potsdam. He also won the 2016 University of Maryland Opera Competition and was commissioned to compose an adaptation of Oscar Wilde’s short story, The Young King, with librettist Tom Rowan for the young artists of the Maryland Opera Studio.
He is currently working on a book of cabaret songs with composer/ lyricist Rachel J. Peters and a series of chamber operas with librettist, Stephen Kitsakos. Two of these: An Incident in Sutton Square and The Woman in Penthouse A form part of a trilogy called Single Occupancies: Three Contemporary Opera Theatre Monologues that premiered to critical acclaim in January of 2020 at the Helmerich Theatre in Key West, FL (along with The Other Room by Marisa Michelson and Mark Campbell.) An Incident in Sutton Square will also be staged in April of 2021 at the University of Tennessee Opera Theatre in Knoxville. Hennessy and Kitsakos are currently workshopping The Pleasing Recollection, a theatrical song cycle which chronicles the adventures of a young gay man in New York City in the early 1980's through the lens of his older self.
Strikingly, Hennessy’s path toward composing music began when he came out about a HIV/AIDS diagnosis in the early 1990’s. He was a core member of Positive Music which presented concerts highlighting HIV positive musicians and composers to bring visibility to the crisis in the classical music community during that period. He is still dedicated to telling the story of AIDS, such as in his chamber opera, A Letter to East 11th Street and in several songs contributed to the AIDS Quilt Song Book.