[2][3] He completed his education at the Juilliard School of Music in New York,[4] where he studied composition with Bernard Wagenaar, orchestral conducting with Fritz Mahler and piano with Eduard Steuermann.
[2][3] In 1949 Diez Nieto, along with musicologist Odilio Urfé, founded the Musical Institute of Folkloric Research, an organization dedicated to preserving and disseminating information about the ethnomusicological history of Cuba.
He conducted works by Johann Sebastian Bach, Ludwig van Beethoven, Ignacio Cervantes, Alejandro García Caturla, George Frederick Handel, Joseph Haydn, Felix Mendelssohn, Wolfgang Amadeus Mozart, Eduardo Sánchez de Fuentes and Antonio Vivaldi; and premiered his Organ Concerto, with Manuel Suárez as a soloist.
He also accompanied soloists such as sopranos Emelina López, Yolanda Hernández, Susy Oliva and Lucy Provedo; pianists Frank Emilio Flynn, Julio Hamel, Alberto Joya and Roberto Urbay; violinists Rafael Lay, Armando Ortega, and Celso Valdés Santandreu; flutists Richard Egües and Alfredo Portela; oboist María de los Ángeles Castellanos; guitarist Flores Chaviano; and clarinetist Rubén Noriega.
He never directly quotes from folk music, but creates original music which recalls it; such as in his pieces Los Diablitos (The Little Devils, 1969) based on an Afro-Cuban Abakuá dance, and Yo te pedí un aguinaldo ("I asked you for a Christmas bonus"; "aguinaldo" also refers to a flowering plant common in Cuba) for voice and orchestra.
[9] Other important works include his Piano Sonata, Sudor y látigo (Sweat and Whip), and the Quintet for String Orchestra.