From 1929 to 1945 he worked for the Dutch statistical office and briefly served as consultant to the League of Nations (1936–1938). In 1945 he became the first Director of the Netherlands Bureau for Economic Policy Analysis and left this position in 1955 to focus on education. He spent one year as a visiting professor at the Harvard University and then returned to the Dutch Economic Institute (the successor of the Netherlands School of Economics). In parallel, he provided consulting services to international organizations and governments of various developing countries, such as United Arab Republic, Turkey, Venezuela, Surinam, Indonesia and Pakistan.