Following the end of World War II, he was ordained a priest in 1949 at the age of 22. He was trained at the Pontifical Ecclesiastical Academy (1957-1959) in Rome before he was sent to the Philippines to serve as secretary in the apostolic nunciature in Manila.
Cacciavillan went on to work in the nunciatures in Madrid and Lisbon before he returned to the Vatican in 1968 to take up a post as the head of the Information and Documentation Office for the Secretariat of State.
Paul VI made Cacciavillan a titular archbishop and appointed him to be the apostolic pro-nuncio to Kenya in 1976. He spent five years in Kenya until John Paul II named him apostolic pro-nuncio to India in 1981 and the first apostolic pro-nuncio to the Kingdom of Nepal in 1985.
John Paul II appointed Cacciavillan as the apostolic nuncio to the US in 1990. The prelate remained in the Washington, DC post until 1998 when the pope called him back to Rome to manage Vatican finances.
Cacciavillan was mentioned more than 80 times in the McCarrick report prepared by the Secretariat of State of the Holy See in November 2020.
According to the report, as apostolic nuncio to the US, Cacciavillan received reports that Theodore McCarrick had acted inappropriately with seminarians in the 1990s, but considered the allegations to be “possible slander” and did not investigate further.