As a diplomat, he worked in Spain, France, Soviet Union, United States, Brazil, Colombia, Venezuela and Morocco.
[2] Bernström began his career as an attaché at the Ministry for Foreign Affairs in 1944, with postings in Madrid in 1945, Paris in 1947, Moscow in 1948, and Washington, D.C. later that year, where he became an embassy secretary in 1949.
In 1963, he was appointed envoy to Caracas, with additional accreditation to Port-au-Prince and Santo Domingo from 1964 to 1966.
After a period on reserve in 1971, he served as vice chairman of the Swedish delegation at the United Nations Trade Conference in Santiago in 1972.
He was then appointed envoy to Madrid from 1973 to 1976 and to Rabat from 1976 to 1983, with concurrent accreditation to Banjul, Dakar, and Nouakchott from 1977 to 1983.