Sadao Watanabe was born in Tokyo in 1913. Initially, he began concentrating on the art of Katazome, or stencil printing. Sadao studied under Soetsu Yanagi and Keisuke Serikawa. He won the first prize at the Japan Folk Art Museum in 1947 and the Kokugokai Prize in 1948. In 1962 he had a one-man show at the Portland Art Museum in Oregon and in 1962 his works were exhibited in the Modern Print Show at the Winter Olympics in Sapporo, Japan in 1972.
Sadao taught printmaking in Minnesota and Oregon. In 1976, at the invitation of the Lutheran Church, Sadao visited America again. He received an honorary Doctor of Fine Arts degree from Linfield College in Oregon in 1981.