Giulio Fossi was born in Florence and graduated with a degree in Economic Geography from the University of Florence and subsequently won a scholarship in regional planning in Sicily from the Associazione per lo sviluppo dell'industria nel Mezzogiorno (SVIMEZ). He was appointed assistant to Professor Pasquale Saraceno in Greece to liaise with the Greek authorities who were cooperating with Saraceno in the elaboration of the first 5-year development plan for Greece.
In 1959 Fossi was recruited by the Organisation for European Economic Cooperation (OEEC) in Paris to work on their European Productivity Agency (EPA) programme for the southern European countries (Italy, Greece, Turkey, Spain and Portugal). In 1961 with the transformation of the OEEC into the Organisation for Economic Cooperation and Development (OECD) with the active participation of Canada and the United States, Fossi joined the Development Assistance Committee. Almost immediately the OECD offered Fossi the possibility to complete a Master’s Degree in Public Administration at Harvard University.
On his return to Paris in 1963, Fossi was transferred to the Development Centre, which was created by the OECD with the assistance of Japan, to serve as a "bridge" between developing countries in Africa, Asia and Latin America. He remained in the Development Centre until his retirement in 1998, with the exception of two years, 1969-1971 which he spent in Washington attached to the World Bank, offering technical assistance in the economic planning of African, Caribbean and Pacific Countries (ACP). Fossi’s time spent in the US provided him with expertise and knowledge in the development field which he was able to utilise when he returned to the Development Centre in Paris where he took up the position of Director for External Relations. In this post, he forged relationships with research agencies in the ACP countries and in parallel with the OECD member countries, the so called "Civil Society".