John Duff (1895–1958) was a Canadian race car driver.
John Duff may also refer to:
John Duff (counterfeiter) (1759–1799), American counterfeiter, hunter, and scout John Duff (singer) (born 1988), American pop singer John B. Duff (born 1931), former commissioner of The Chicago Public Library John Finlay Duff (1799–1868), captain of ship Africaine and businessman in South Australia John Wight Duff (1866–1944), Scottish classicist and academic