In 1963 he was first elected member of Tweede Kamer, the lower house of the Dutch parliament, as representative of Katholieke Volkspartij (KVP). From 1963 to 1967 he was member of the European Parliament. He served as Minister of Agriculture (1967-1973), during which time he served as the Dutch Coordinator of Affairs and Provision of Aid and Assistance Concerning Suriname and the Netherlands Antilles from 1972-1973; thereafter he was appointed European Commissioner (1973-1977). From 1977 to 1986 he was the chairman of the Rabobank.