The transaction is due to close in August.
Lekela has more than 1GW of operational wind capacity in Africa, including wind farms in South Africa, Egypt and Senegal.
The firm was set up in 2015 as a joint venture, owned 60% by Actis and 40% by a Mainstream-led consortium.
Mainstream CEO Mary Quaney said that much of Africa is “acutely vulnerable” to climate change and added that Lekela’s wind portfolio and pipeline “will continue to have a positive impact for decades to come”.
Actis’ head of energy infrastructure Lucy Heintz said: “Lekela Power [is] strongly positioned for its next phase of growth as an acknowledged sustainability leader supplying much-needed clean energy to communities across Africa.”
AFC president and CEO Samaila Zubairu said that the Lekela acquisition is central to its plans to build a 3GW renewable energy platform.
Infinity and the AFC aim to more than double their joint operating assets – which stand at 1.4GW after the Lekela deal – in the next four years.