Adam Porter and his wife Angela MacLochlainn are now hoping the discovery can be preserved and marketed to tourists.
Most of the rocks were documented in the 1970s by a Dutch archaeologist. They feature circular markings carved into the rock 3,000 years before Christ. But 40 years of growing gorse had hidden them away.
"It was just breathtaking to see them for the first time," said Adam after his expedition in the townland of Magheranaul on the Isle of Doagh, Inishowen.
"There are more of these pieces of rock art here than in the Ring of Kerry."
Together with his father-in-law Liam, wife Angela and their daughter Faolain, they carefully removed gorse and used hundreds of litres of water to reveal the rocks.
Adam, a member of a local heritage group, says the find is already sparking interest amongst tourists.
"We've had people from France and Germany online asking if they can visit to see the rocks," he said.
"It's one of the largest areas of Neolithic rock art in western Europe and people really want to see them. With a bit of work, they could become tourist attractions," he added.
The National Monuments Service is investigating the discovery. "We will look at how best to proceed for the further protection of these monuments," said a spokesman.