After the required theological studies, which he began in his home diocese of Piacenza, Silvio Oddi was ordained a priest on 21 May 1933 in Rome. After three further years of study at the Pontifical Ecclesiastical Academy in Rome, he entered the diplomatic service of the Holy See in 1936 and was assigned to the Apostolic Delegation to Iran until 1939. From that year until 1945 he held a similar post in Syria and Lebanon, then in Egypt (1945-1948), and France (1948-1951). He became head of the Apostolic Nunciature to Yugoslavia in 1951. On 30 July 1953, Pope Pius XII named him Titular Bishop of Mesembria and Apostolic Legate for Jerusalem, Palestine, Transjordan and Cyprus. On 27 September of the same year, he received episcopal ordination from Angelo Giuseppe Roncalli, the future Pope John