The discovery has been likened to finding a treaure trove
Researchers made the find after being tipped off by a local sheep herder. They discovered a mural with 55 panels showing the story of Buddha's life.
The mural was uncovered in March, with the team using ice axes to break through a snow path to reach the cave.
The find was in the Mustang area, 250km (160 miles) north-west of Kathmandu.
"What we found is fantastically rich in culture and heritage and goes to the 12th century or earlier," American writer and conservationist Broughton Coburn told the AP news agency.
Mr Coburn said the main mural measured around 8m (25ft) wide, and each panel was about 35cm (14in) by 43cm (17in).
It was set in sheer 14,000ft (4,300m) cliffs in Nepal's remote Himalayan north.
The team of international researchers - including film makers, climbers and archaeologists - from Nepal, Italy and the US were told of the works of art by a sheep herder.
In passing conversation he said that he had seen a cave with old paintings in it several years ago as he took shelter from the rain.
It turned out to be a treasure trove of Buddhist art, consisting of a complex of caves several hours walking distance apart.
The team says that there are around 20 openings in each complex, with multiple floors connected by vertical passages with rudimentary hand and footholds, requiring some climbing skill to negotiate.
Besides the main mural, other paintings were discovered which the team believes are marginally older.
A nearby cave had manuscripts written in the Tibetan language, which were photographed by the team to be translated later by experts, along with pre-Christian era pottery shards.
"Who lived in those caves? When were they there, when were (the caves) first excavated and how did the residents access them, perched as they are on vertical cliffs?" asked Mr Coburn.
"It's a compelling, marvellous mystery."
Mr Coburn said that his team would try and find answers by performing limited excavations, in addition to collecting and cataloguing the manuscripts.
The team has refused to divulge the exact location of the caves to prevent the possibility of visitors disturbing the centuries-old art.
The expedition spent three weeks in the remote mountainous area, which for centuries has been used as a major transit route between Nepal and Tibet.
Mr Coburn said that there were other mounds which may hide further treasures.He said the artefacts had remained unpillaged partly because the area north of Mount Annapurna has, until recently, been inaccessible.