With a professional career mostly identified with the Cuban bolero, Castro had the opportunity to sing with Tony Bennett, Paul Anka, José Feliciano, Johnny Mathis, and Liza Minelli, among other popular artists.

In 1971, a song called "Y Después Del Amor," composed by his brother Arturo Castro, allowed him to win the Rio de Janeiro's Festival. A second major achievement came in 1975 in Puerto Rico with Armando Manzanero's "Felicidad." In addition, Gualberto Castro twice won the OTI Festival and his talent was awarded in 1978 at Paris' International Festival after being voted the Best Performer. ~ Drago Bonacich