 De Clercq served in various coalition governments.He was secretary of state for the budget (1960–1961), deputy prime minister and minister of the budget from 1966 to 1968, deputy prime minister and minister of Finances in 1973–1974, minister of Finances in 1974–1977 and deputy prime minister in 1980.De Clercq served as president of various international monetary instances and as president of the then liberal party PVV.