Erkko was the Minister of Foreign Affairs between 1938 and 1939, as the Finns negotiated with the Soviet Union. The Soviets demanded exchange of areas with Finland. Erkko did not want to make any concessions. As the Winter War started, Väinö Tanner assigned a new government and decided to appoint himself as foreign minister. Between 1939 and 1940 he was a chargé d'affaires in Stockholm.