Born in Rostock, Germany, Neumann studied at the United State Schools for Free and Applied Arts in Berlin. After serving in the German army during World War I, he taught art in Berlin. He moved to the Unitied States as an adult, settling in Milwaukee in 1926 and receiving American citizenship in 1933. He studied under Hans Hofmann in Gloucester, Massachusetts. Neumann taught at the Layton School of Art in Milwaukee (1929–1930), the Art Institute of Chicago, the Wisconsin State Teachers College (1930–1959), and the Ox-Bow Summer School of Painting at Saugatuck, Michigan. Von Neumann was a member of the Wisconsin Painters & Sculptors, and its president in 1931 and 1932. He was also one of the founding members of the Wisconsin Watercolor Society.
