Born in Casoria on 16 April 1913 to the town's mayor and pharmacist,[1] Antonio del Guidice was ordained a priest in Rome in 1936.
He earned a degree in civil and canon law in 1940[1] and then entered the diplomatic service of the Holy See as the protege of Cardinal Secretary of State Luigi Maglione, who came from the same home town.
[1] His next assignments took him Ecuador in 1952, Formosa from 1958 to 1960, to India in 1961, and to the Dominican Republic as Chargé d'affaires, when the regime of Rafael Leónidas Trujillo had just been overthrown by the military.
[1] On 18 April 1962 he was appointed Apostolic Delegate in Korea by Pope John XXIII, and on the 29 June he received his episcopal consecration as titular archbishop of Hierapolis of Syria from Cardinal Amleto Giovanni Cicognani.
In 1989, the government of Iraq decided not to allow non-Islamic religious followers to continue to live in the country, del Guidice succeeded in having the policy reversed.