Donald Sinclair (January 9, 1899 – October 5, 1978) was an American farmer and politician.
He served in the United States Navy during World War I and then received his bachelor's degree from the University of Minnesota in 1924.
Sinclair lived in Stephen, Minnesota with his wife and family and was a farmer.
Sinclair served in the Minnesota Senate from 1947 until 1972 and was a Democrat.
Ne died from cancer in a hospital in Warren, Minnesota.