John was educated at Eton and Cambridge and later became a fur broker.
Cobb became interested in automobile racing after World War I but did not gain international fame until Sept. 15, 1938, at Bonneville Salt Flats, Utah, when he set a new automobile speed record of 350.2 mph (563.6 km/h) (the official record is an average of two runs in opposite directions over a measured mile). On Aug. 23, 1939, at Bonneville, he again broke the record, setting a mark of 368.9 mph (593.7 km/h). During World War II Cobb served with the Royal Air Force and as a ferry pilot, but after the war he returned to racing automobiles and, later, motorboats. He set a new automobile mark of 394.196 mph (634.397 km/h) on Sept. 16, 1947, at Bonneville, and on his first run did 403.135 mph (648.783 km/h) to become the first man ever to exceed 400 mph (640 km/h) on land. On Sept. 29, 1952, at Loch Ness, Scotland, Cobb attempted to break the motorboat speed record of 178.497 mph (287.263 km/h) in a specially built jet-propelled boat. On his first run he averaged 206.89 mph (332.96 km/h), the first time 200 mph (320 km/h) had been bettered on water, but just after completing the run and before the officially required return run could be made, his motorboat broke apart and Cobb was killed.