Born in the north of Norway to a fairly distinguished family, he soon became interested in politics and history. Starting his political career in the Liberal Party, he switched to the Labour Party around the turn of the 20th century. He represented that party in the Bærum municipal council for parts of the interwar period. He was never elected a member of Parliament, but served nonetheless as Norwegian Minister of Foreign Affairs from 1935 to 1940, as part of the government-in-exile following Germany's invasion of Norway. In the latter capacity he sought to preserve Norway's neutrality in the Second World War, a decision that garnered him political infamy. Growing discontentment with Koht's political decisions ultimately led to his exit from the cabinet. After the war, however, he returned to his academic career track and wrote major works in the 1950s and 1960s.