Career
In 1922 Hynninen became an official in the foreign ministry and initially worked in the Finnish consulate in Saint St. Petersburg. Later he became the ambassador to Latvia and Estonia in the 1930s. After the Continuation War, Hynninen"s career continued in the new political circumstances.
He served as the ambassador to Denmark from 1946 until his retirement in 1953.
In his days of pension Hynninen served as Foreign Minister in neutral cabinets from 1957 to 1958.