Spaak entered politics in 1932 for the Belgian Workers' Party (later the Belgian Socialist Party). He became Prime Minister of Belgium in 1938 and held the position until 1939. During World War II, he served as Foreign Minister in the Belgian government in exile under Hubert Pierlot. After the war, he twice served the position of Prime Minister, first for under a month in March 1946 and again between 1947 and 1949. 