Johannes Westhoff studied at the Royal University of Leiden and then at the Institut des Sciences Politiques in Paris, where he obtained a doctorate in Law. He began his legal career in The Hague (1948-1951) and then specialised in the United States, in New York. From the first year (1951-1952) until 1955 he served as registrar of the Constitutional Committee of the Ad hoc Assembly Instructed to Work out a Draft Treaty setting up a European Political Community. Later, he entered the Dutch Ministry of Agriculture (1955-1958), but he also held the position of secretary in the intergovernmental committee that was to work for the establishment of the Euratom and the Common Market. He was also a member of the Dutch delegation. In 1958, he took office in the Commission of the European Economic Community and in the European Commission Directorate-General for Agriculture. From 1966 to 1973 he was Director for General Affairs in the European Commission Directorate General for Development and from 1973 to 1976 he assumed a role in the same DG as Director/Legal Advisor. During the following years, he represented the Commission in external delegations in Jamaica (1976-1980), and in Ghana (1980-1983).