The projects are the 140MW Kangnas, and the 110MW Perdekraal East developments located in the Northern Cape and Western Cape respectively.
The contracts have been awarded as part of South Africa's Renewable Energy Procurement Programme (REIPPP). Mainstream said their investment value was a combined €420 million.
On 16 April the Department of Energy (DoE) issued a statement promising to "expand procurement of renewable energy", including an initial commitment to more than 9.2GW in the short and medium term.
There has been relatively little indication of how much will be wind. However, Mainstream managing director for onshore Barry Lynch said the country was was ideal for wind power.
He said: "Our pipeline [in South Africa] is predominantly wind. The wind profile meets the country's needs quite well. So we're confident the government will support it.
"The large-scale projects can support wind quite well and deliver a tariff that can't be touched by conventional generation."
He added the capacity factor in the country was around "the mid-40s (MWhs)".
Speaking about the ideal machines for South Africa, Lynch said the South African market was ideally suited to low-to-medium machines with big rotors and capable of high hub heights.
A major factor in the picking of the sites was transportation and the ability to construct on-site.
"Also a lot of engineering goes into the siting of the machines, whether that's 2.5MW or 3MW," said Lynch. "You have to put a huge amount of effort in to get it right because the market is so competitive."