The project will be located in the Gulf of Suez, near Aswan, and will be placed under Egypt's FiT scheme.
Overall, Lekela is looking to develop 1GW across Africa over the next five years. According to Mainstream, Lekela's Egypt pipeline includes a 250MW wind power plant in Gabal Elzeit.
Mainstream owns 40% of Lekela and has partnered with Actis on a similar JV initiative in Chile.
Speaking about the deal, Sherif Elkholy, Egypt Director at Actis said: "Lekela is Actis's eighth energy platform; and our third partnership with Mainstream Renewable Power.
"Expanding Lekela's pan-African presence into Egypt reiterates and reinforces Actis's commitment and track record on the ground in Egypt over the last 13 years; we look forward to announcing more successes for Lekela and Actis in Egypt in due course."
Earlie this year, Actis invested $230 million in an Indian subsidiary with the aim of building 800MW in the country.