William Duff Jr. (April 28, 1872 – April 25, 1953) was a merchant, ship owner and political figure in Nova Scotia, Canada. He represented Lunenburg from 1917 to 1925, Queens—Lunenburg from 1925 to 1926 and Antigonish—Guysborough from 1927 to 1936 in the House of Commons of Canada as a Liberal member. Duff represented Lunenburg division in the Senate of Canada from 1936 until his death in 1953.