He composed, over the course of his life, over 200 works, most of it for guitar. A number of his works survive as recordings, including Appalachian Dreams, performed by Sharon Isbin, and a CD of his work performed by Antigoni Goni.
Duarte was a chemist by training, but gave up the profession in the early 1970s to devote himself to music. A fan of both classical music and jazz, he was involved with the Spanish Guitar Centre and was friendly with such musicians as Andr_s Segovia and Ida Presti. Segovia recorded some of Duarte's compositions.
As a teacher, he traveled all over the world to master classes and summer schools.
In addition, Duarte was a longtime contributor to Gramophone magazine: writing about guitar, Baroque, and Latin American music: as well as contributing to Soundboard, Classical Guitar, The New Grove Dictionary of Music and Musicians, and countless liner notes.