Attended Omaha University, The University of Nebraska-Lincoln, the Swedish Royal Academy in Stockholm, and the Heatherly School of Art in London. He received an Honorary Doctor of Fine Arts from Creighton University in 1972. He was the State Director for the Iowa Federal Art Project from 1941 to 1942. From 1938 to 1950, he was the art critic for The Omaha World Herald. He was then the Executive Secretary of the Nebraska Arts Council from 1966 to 1974. Thiessen was a founding member of the Nebraska Art Collection and a great supporter of the mission of the Collection and the Museum of Nebraska Art.