As an academic, Voionmaa contributed to introduce economic and geographic perspectives into Finnish history writings. He has studied the medieval times and the rise of the modern urban industrial society. He was also one of the founders of the School of Social Sciences in 1930 that eventually became the University of Tampere.
Voionmaa was one of the senators in the Tokoi senate in 1917 before the declaration of independence. Later he served as the Minister of Foreign Affairs in the cabinet of Väinö Tanner 1926-1927. He was also the Minister of Trade and Industry in the Cajander 3rd cabinet 1937-1939, and also briefly the Minister of Foreign Affairs in 1938. Voionmaa's experience in foreign affairs grew while he was a member of the Finnish delegation to the League of Nations.