His birth date is unknown but he was baptized as Francisco Bartolomé Sanz Celma in the church of Calanda de Ebro, Aragon on 4 April 1640 later adopting the first name "Gaspar".
After gaining his Bachelor of Theology at the University of Salamanca, Gaspar Sanz travelled to Naples, Rome and perhaps Venice to further his music education. He is thought to have studied under Orazio Benevoli, choirmaster at the Vatican and Cristofaro Caresana, organist at the Royal Chapel of Naples. He spent some years as the organist of the Spanish Viceroy at Naples.
Sanz learned to play guitar while studying under Lelio Colista and was influenced by music of the Italian guitarists Foscarini, Granata, and Corbetta. When Sanz returned to Spain he was appointed instructor of guitar to Don Juan (John of Austria), the illegitimate son of King Philip IV and Maria Calderon, a noted actress of the day.