The big cats historically occupied vast areas amounting to roughly 13.5m sq miles (35m sq km) including large parts of Africa, the Middle East, and Asia.
Today, they are restricted to just 3.3m sq miles, according to the new findings.
Scientists made the discovery after spending three years reviewing more than 1,300 sources of data on the animal’s historical and current range.
The research — published in the journal PeerJ — represents the first attempt to produce a comprehensive analysis of the leopard’s range status.
While the leopard as an entire species is not said to be threatened, two sub-species — the Javan and Sri Lankan leopard — are classified as critically endangered, and endangered.
Conservationists fear that the animal faces a multitude of growing dangers in the wild.
Leopards have almost completely disappeared from several regions across Asia, including much of the Arabian peninsula and large areas of China and South-East Asia.
African leopards also face considerable threats, especially in the north and west of the continent.
Worldwide, around 17% of existing leopard habitat is under some kind of formal protection.
Lead author Andrew Jacobson, from the Zoological Society of London’s Institute of Zoology, said: “The leopard is a famously elusive animal, which is likely why it has taken so long to recognise its global decline.
“This study represents the first of its kind to assess the status of the leopard across the globe and all nine subspecies.
“Our results challenge the previous assumption that in many areas, leopards remain relatively abundant and not seriously threatened.
“This underscores the pressing need to focus more research on the less-studied subspecies, three of which have been the subject of fewer than five published papers during the last 15 years.”
Leopards can survive in human-dominated landscapes, provided they have sufficient cover, access to wild prey and are tolerated by local people, said the scientists.
But in many areas their habitat has been converted to farmland and native herbivores replaced with livestock.
Conflict with livestock owners, the illegal trade in leopard skin and body parts, and trophy hunters are also said to have contributed to the cat’s decline.