The announcement by English Nature means the 2,500 acre park has become London's largest National Nature Reserve and one of the "finest wildlife sites in England".
Richmond is among the UK's top six sites for its rare beetles, 1,000 species have been counted, making up over one quarter of all beetle species in Britain.
"Richmond Park is bursting with biodiversity and stuffed full of history," said English Nature chairman Baroness Young of Old Scone.
"This is the highest honour English Nature can bestow and we are delighted to declare Richmond Park as a National Nature Reserve."
The announcement will fuel the argument for cutting traffic in the park.
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