John Andreassen was born in Bloomer, Wisconsin, and studied at Tulane, Wisconsin (Ph.B., 1931) and Louisiana State (M.A., 1935) Universities. His career as an archivist began in 1937 with his appointment as regional director of the Historical Records Survey of Louisiana. He supervised service projects for the Work Projects Administration from 1941 to 1943, and from 1943 to 1950, he was the administrative officer of the Federal Works Administration. As a displaced persons specialist for the United Nations Relief and Rehabilitation Agency (UNRRA), he worked in London (1944-1945), Sweden (1945), and on a relief mission to Austria (1945-1946). From 1946 to 1952, Andreassen was Director of Administration of the Library of Congress and held the chair of aeronautics there from 1952 to 1953. He returned to Louisiana to become Associate Director of the state archives survey (1955-1956), and later, Director of the Louisiana Archives and Records Commission (1958-1960). After completing a paperwork survey for the New Orleans government (1961), Andreassen came to Montréal as archivist of the Canadian National Railway. He has also acted as a consultant in archives administration as a partner in the Records Management Company, Montréal. From 1968 until his retirement in 1977, he was McGill University Archivist. Andreassen was one of the founders of the Society of American Archivists and of the Montreal Chapter of the Association of Records Managers and Administrators.