After an education at the Christian Brothers' College in Toowoomba, Leahy initially worked as a railway clerk before leaving to become a freelance timber cutter.
He also made two pioneering airplane flights into the western highlands, discovering the Wahgi Valley, taking thousands of photographs and movie film.
He concluded that Leahy had acted in self-defence, and viewed such deaths as inevitable if prospectors were afforded the right to explore territories beyond the control of the colonial authorities.
During the Second World War he joined the Royal Australian Air Force as a flight lieutenant and was assigned to the US chief engineer to build an airstrip in Telefomin.
The 1983 award-winning documentary film 'First Contact' is about the exploration of the Wahgi Valley and Mount Hagen in Papua New Guinea based on much of Leahy's footage.