He was baptised at his parish church in San Cristobal on February 7, 1903, by Father Marcelino Herrero-de Dios (Registered in Box 19 of Baptisms, Folio 387, number 1260).
He was assigned to the parish of Santo Ángel on February 15, 1939, and on April 11, 1940, Vice-Rector of the Seminary and six days after that Chaplain of the Sagrado Corazón de Tejadillo.
Diaz-Cia was elevated to Bishop of Pinar del Río on December 26, 1941, by Pope Pius XII.
On that same date he was named Apostolic Administrator of Pinar del Río and remained in that position until January 16, 1960, when Mons.
Promoted to Titular Archbishop of Petra di Palestina and named Coadjutor sedis datus of Havana on November 14, 1959.
Diaz-Cia renounced his titular see and assumed the title of Archbishop Emeritus of the Archdiocese of Havana on December 26, 1970.