Andersen finished his degree in political science in 1940, worked for Statsradiofonien from 1935 to 1950, and was the headmaster of the "Workers' Folk high school" in Roskilde from 1950 to 1957.

[2] Andersen served as Minister of Education in the Cabinet of Jens Otto Krag from 1964 to 1968.

[3] In 1970, Andersen left the Folketing, but was appointed Foreign Minister under Jens Otto Krag and later Anker Jørgensen, from 1971 to 1973 and again from 1975 to 1978.

[citation needed] At a NATO council in December 1972, Andersen received heavy criticism from Sir Alec Douglas-Home, William P. Rogers, and NATO's Secretary General, for Denmark's eight percent reduction in their defense budget.

[citation needed] This was at a time when the more powerful nations of Europe were calling for an increase in military spending.