degree with distinction and a performer's certificate, Fennimore entered the Juilliard School of Music in Manhattan that autumn as a student of Rosina Lhévinne, receiving an M.S.

[21] Since the early 1970s he has devoted his energies more exclusively to his compositional efforts,[22] new works introduced and often performed by mezzo-soprano Joyce Castle, cellist Ted Hoyle, harpsichordist Elaine Comparone and pianists Larry Graham, Dennis Helmrich, Jeffrey Middleton, Dan Teitler, Marthanne Verbit and Juana Zayas.

"[30] Long maintaining one home in Manhattan and another in upstate New York, Fennimore and Gordon Hibberd were among the first tenants at the landmark Westbeth Artists Community Housing in Greenwich Village.

[8] Fennimore's music, especially that featuring the keyboard, is often of a technical sophistication and chromatic complexity that stretch the Western tonal tradition it rises from; such exotica as Cathay and Sea of Sand, evoking Chinese and Middle Eastern idioms respectively, similarly expand on it in a "continual metamorphosis" of his style.

[31] Beyond a nostalgic or "bittersweet" lyricism often commented on,[32] an additional distinguishing component of Fennimore's style is an elevated wittiness and "seriously playful sport"[33] exemplified by his satiric take on language instruction, the aforementioned Berlitz: Introduction to French, and Foxtrot, a fanciful tribute to bygone popular musical genres.