During the Second World War, Captain Leather served with the 1st Canadian Parachute Battalion, Canadian Army in England and Europe. He was badly injured in a practice jump when his parachute failed to open. He rejoined his Battalion for D-day. He served in Europe during World War II with the Toronto Scottish and Royal Canadian Artillery. He wrote a manual for the Home Guard called "Combat without Weapons". He worked as an insurance broker in England and was secretary of the Central London branch of the Association of Supervisory Staff, Executives and Technicians.