He studied composition at the Curtis Institute of Music in Philadelphia and at summer festivals in Aspen and Tanglewood.
Hennagin began his professional career as a Hollywood composer and arranger working in film and television.
[1] Notable compositions include soundtracks for The DuPont Show of the Week and the television series Voyage to the Bottom of the Sea,[2] ballet scores for the Lester Horton Dance Theater[3] in Los Angeles, and his Duo Chopinesque for Percussion Ensemble and Walking on the Green Grass for Choir are performed frequently.
He received awards from American Society of Composers, Authors and Publishers (ASCAP) recognizing his continued commercial influence and success, and he was named National Composer of the Year in 1975 by the Music Teachers National Association.
Shortly before his death, Ohio State University honored him with a week-long festival and he traveled to New York City where The Gregg Smith Singers premiered a new choral work at Carnegie Hall.