In 1964, he was admitted to the Pontifical Ecclesiastical Academy and on 1 January 1967 he entered the diplomatic service of the Holy See. Romeo worked in the nunciatures in the Philippines, Belgium and Luxembourg and European Community, Venezuela, and Rwanda and Burundi. In 1967, he was called to the Council for Public Affairs of the Church in the Secretariat of State. At the same time, he worked as director of the "Casa Internazionale del Clero" and was regional assistant for the Lazio of the AGESC.