John Francis Duff was a Canadian racing driver. He is best known for winning the 1924 24 Hours of Le Mans.

The 1924 24 Hours of Le Mans was the 2nd Grand Prix of Endurance, and took place on 14 and 15 June 1924. It was the second part of three consecutive annual races for the Rudge-Whitworth Triennial Cup, as well simultaneously being the first race in the new 1924-25 Rudge-Whitworth Biennial Cup.