Several times prime minister of Belgium (1949 - 1950, 1958 - 1961, 1968 - 1972), he was confronted with major ideological and linguistic conflicts (the controversy over king Leopold III in 1950, the "School War" in 1958, the split of the University of Leuven in 1970). He oversaw the first steps towards the regionalization of Belgium (constitutional reform of 1970).