Van Boetzelaer van Oosterhout's father was mayor of Leusden. After studying at Utrecht University and obtaining a Master of Laws at the University of Amsterdam in 1921, he held many diplomatic positions abroad including in Washington DC (1926–29), Mexico City (1929–30), Brussels (1930-1934), and Berlin (1934-1940). After the German invasion of the Netherlands he led the diplomatic affairs in London from May to August 1940 after which he became ambassador for the Netherlands in Washington DC.