A renowned twentieth-century historian, he is especially known for his work on the subjects of Minnesota and Norwegian settlements in America. His published works include The Competition of the Northwestern States for Immigrants (1919) and Building Minnesota (1938).
He was the superintendent of the Minnesota Historical Society as well as the managing editor of the Norwegian-American Historical Association.
The University of Minnesota named its geography department building in Blegen's honor.
He was born in Minneapolis, Minnesota to Norwegian immigrant parents. His older brother, Carl Blegen, was a notable archaeologist.
He and Spalding Gray were both Guggenheim Fellowship recipients.