The Brown Caps started the year by announcing the arrival of Proteas Test captain Graeme Smith, who has since suffered a season-ending injury, while Australian great Ricky Ponting is currently filling the overseas position.
Duminy, 29, will take over from Ponting at the end of South Africa's tour of Sri Lanka and is available for six LV= County Championship matches as well as the end of the Yorkshire Bank 40 and Friends Life t20 competitions.
"I am really chuffed to have signed with a great club like Surrey," said Duminy.
"I love the UK and I really look forward to working with Chris Adams and the rest of the team."
Surrey team director Adams added: "I am delighted that JP Duminy has agreed to join Surrey for what will no doubt be an exciting and important period of our season. We are happy to be welcoming him to the club and look forward to him making a big contribution during his time here."
Meanwhile, Australian seamer Mitch Claydon has joined Kent on loan from Durham.
The 30-year-old, who has been with Durham for six years, has not made a competitive appearance in the first team this season and will drop a division to play for Kent.
The initial deal expires on July 10, with an option in place to extend Claydon's stay.
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