According to Dr Paul Wilkinson, founder of the Kent Archaeological Field School, it is the first of its kind to be found in Britain.
The theatre with a nearly circular cockpit-style orchestra and a seating capacity of 12,000, was found in Faversham, in the back garden of Wilkinson's school, the 'Daily Mail' reported.
The site shows activity dating back to the Bronze Age, however it is the Roman theatre - which would have been used for religious occasions - that has really excited history buffs.
In order to preserve the unique find for future generations, Wilkinson has applied for an ancient monument status for the site.
"It really is an amazing find, the first one in Britain, and it is just beyond my garden. This is a unique and wonderful discovery, not only for Faversham but for all of Britain," Wilkinson said.
"The theatre could have held 12,000 people and we are going to request for it to become an ancient monument site because it is so important and we can preserve it for future generations.
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"It would have been a religious sanctuary for the Romans. They would have held religious festivals there. It is called a cockpit theatre," he said.
"There are 150 of them in northern Europe, but none in Britain until now. We were not expecting it," said Wilkinson.
Investigations began on the site in 2007, but the results have only just been released.
Wilkinson believes the site is the only known example in Britain of a Roman rural religious sanctuary, with a theatre actually built into the hillside. Two temple enclosures were also found nearby along with a sacred spring.
"If the full analysis of the results does confirm that the site on the outskirts of Faversham is a Roman rural theatre, it would be a most remarkable find," English Heritage spokesman Debbie Hickman said.
Wilkinson has led archaeological digs in Kent for more than a decade. In September he led a team that found an ancient ceremonial site the size of Stonehenge on the North Downs, the report said.