Medieval graves found during dig in England
The discovery, thought to be the largest of its kind outside of London, was made during excavations for a £350m shopping centre extension.
The wall trenches of St Peter's Church were also found.
Peter Liddle, Heritage Services, Leicestershire County Council said the discovery would show "a slice of the medieval inhabitants of Leicester".
The church was torn down in the 16th Century and the timber and stone was used to build the grammar school on High Cross Street.
We think, probably outside London, this must be one of the largest parish graveyards ever excavated
Richard Buckley, director of University of Leicester Archaeological Services
"We have known from documents that the church existed - and we knew how big it was - but this confirms all that," he said.
He said the dig was kept under wraps for months to avoid attracting onlookers.
The church was built in the late Saxon era and stood for about 500 years.
University of Leicester archaeologists behind the excavation will start a two-year study of their find.
Communal graves and a high number of child skeletons already provide evidence of high infant mortality and contagious diseases, said Richard Buckley, director of University of Leicester Archaeological Services.
The burial ground had a relatively short history - from the 12th Century to the church's demolition in 1573.
Mr Buckley said: "We think, probably outside London, this must be one of the largest parish graveyards ever excavated.
"It's very rare that we get a look at a population itself. It's quite a tightly dated group."
The excavation will also tell more about a church with a particularly grisly secret.
Mr Buckley added: "In the 14th Century, a bell-ringer turned up late for Christmas Eve and he was murdered by the vicar.
"He stabbed him in the head with a knife and killed him."
The site, which was excavated between April and November last year, will soon be the location for a John Lewis store.
The skeletons will eventually be buried at Gilroes cemetery in Groby Road.