A precocious teen, Castelnuevo
studied at the Florence Conservatory, earning diplomas in piano and composition. An association with Casella
helped him to early fame, enabling him to live in Florence as a freelance composer and pianist. A Jew, Castelnuevo
was forced to flee to the USA in 1939 where he took American citizenship and pursued a career in film composition. He was a very prolific composer, creating works of a wide range of quality. His early songs and piano pieces were his finest work, most notably his settings of 33 Shakespeare Songs. He also wrote operas, concertos and a large number of works for guitar.