The event, which takes place 4-5 September 2014, will see up to 60 world leaders visit the South Wales venue. Next year marks the first time the UK has hosted the Nato Summit since 1990.
Cameron said: "The Nato Summit is a great opportunity to showcase the modern, successful Wales. So we are going to be holding it at Celtic Manor but also using other sites as well, including in Cardiff.
"We've had the G8 in Northern Ireland, we've had the Olympics in London and we've got the Commonwealth Games in Scotland in 2014.
"It is now Wales's turn for one of these big events. This is a wonderful opportunity for Wales, and South Wales, and I'm delighted to make the decision to bring the Nato Summit here."
The venue has hosted an array of international events, including the Ryder Cup in 2010.
Sir Terry Matthews, the venue's chairman, said: "We are honoured to be welcoming such a momentous and prestigious global event to Wales and look forward to showcasing the Resort on the world stage."