"It's Porsche South Africa that has been the successful bidder," said auctioneer Joff van Reenen, adding that it was South Africa's highest auction price on a single lot.
The purchase by the luxury car company will come as a relief to motorsport fans who feared that the 72 hectares of prime land north of Johannesburg would be bought by property developers who would scrap the famed circuit.
"They are going to keep it as a track. I believe they may develop around the track, which will enhance the value for the lot," said Lance Chalwin-Milton of High St Auction Company.
"It will remain in motor sports in South Africa which is great — a Grand Prix would be nice!"
Porsche, one of seven registered bidders, bought the Kyalami racetrack for 205 million rand ($19.5 million).
"The most important thing is that Kyalami has been saved for racing and we'll continue to operate it as a racetrack," said Porsche South Africa CEO Toby Venter.
"There are some synergies with Porsche that we can integrate now and into the future but that doesn't mean that other manufacturers will not also be accommodated," he told the Eyewitness News agency.
The fast 4.26 kilometer circuit hosted Formula One races from 1967 to 1985, when it was axed from the world championship due to a sports boycott against the former racist apartheid regime.
Local hero and former world champion Jody Scheckter won the South African Grand Prix there in 1975.
Formula One was revived at Kyalami in 1992 and 1993 in the wake of the release from prison of liberation icon Nelson Mandela, but the bankruptcy of a sponsor put an end to the program.
Frenchman Alain Prost was the last winner at Kyalami in 1993.
The circuit hosted its last international competition in May 2010 with the sixth race of the World Superbike Championship.