Enlisted at the age of 19 in the Royal Canadian Air Force. After flight training, he joined 402 Squadron in November, 1941 and was commissioned in May, 1942. He was posted to the Mediterranean theatre in January, 1943 and joined 72 Squadron in March, 1943.
A good pilot with hunting skills honed in the areas around his hometown of Taber, Alberta, Keith scored a total of 8.5 victories and two probable victories as well as two "damaged". Keith downed mostly fighters: 5.5 Messerschmitt Bf 109 fighters, 1 Macchi C.200 fighter, and 2 Junkers Ju 88 bombers. On two occasions, he had a two kill day. In one 48 hour period he had a total of 3.5 kills.
While strafing ground targets near Sicily on Aug 4, 1943, Keith's Supermarine Spitfire Mk V was struck by anti-aircraft fire and he was forced to bail out. When bailing out at 2,000 feet (600 m), the tailplane of the Spitfire struck Keith, breaking both his legs. His parachute did not open until 300 feet (100 m) and he landed in the sea. He was picked up quickly by Air Sea Rescue but died of his injuries shortly after.