Born in Chalk River, Ontario, Leach left high school in 1940, to work as a car-checker for the Canadian Pacific Railway Company.
After the war, Leach went back to high school, and in 1946, enrolled at the University of Western Ontario, rejoined the RCAF and obtained his medical degree in 1952.
From 1954 to 1966, Leach "was posted to the RCAF Institute of Aviation Medicine at Toronto, Ontario where he worked"[3] in several departments, including the respiratory physiology section.
"[3] Leach was next posted in 1966, to the staff of the surgeon general, as a Group Captain and Director of Medical Staffing and Training.
[5] Major-General Leach was awarded several honours such as the Trans-Canada McKee Trophy (in 1960), which he received for his research in high-altitude physiology, and he was inducted into Canada's Aviation Hall of Fame (in 1974).