[3] He was then incardinated into the Diocese of Greensburg, Pennsylvania, in 1958, and served in parishes and other institutions for twenty years.

From 1964 to 1967 he was a headmaster at St. Joseph Hall Preparatory School in Greensburg, PA.[2] In the 1980s De Andrea served as a representative of the Vatican at the United Nations.

[3][4] On 2 December 1999 he became chargé d'affaires of the Holy See diplomatic presence in Kuwait, Yemen, and the Arabian Peninsula.

[7] On 8 January 2007, Pope Benedict XVI named him a member of the Congregation for the Evangelization of Peoples.

He died in Rome at the age of 86 and was buried alongside his brother Archbishop Giovanni in the Rivarolo Canavese cemetery.