The shares in the Japanese firm’s African subsidiary were sold to Hitachi Power Europe for an undisclosed amount.
“All parties have agreed strict confidentiality about the terms and conditions of the contract,” Hitachi Power Africa said in a statement announcing the deal.
Spokeswoman Yash Bridgmohan said the agreement was concluded on February 1.
The African National Congress’ (ANC) stake in the firm, through its investment arm Chancellor House, had over the past raised questions over a conflict of interest.
Opposition parties had demanded that the company stop doing business with government.
Hitachi Power Europe and Hitachi Power Africa were awarded a contract to install boilers for the country’s mega power plants Medupi and Kusile, which are still under construction.
The coal-fired stations are being built by the state power utility Eskom, which buckled under power demands nearly five years ago, causing crippling countrywide blackouts.
Both the facilities have been marred by delays and the utility said last year it expects their first of the six completed units to come on line in the second half of 2014.
Last year, the minister of public enterprises, Malusi Gigaba, criticised Hitachi for failing to providing quality boilers at Medupi Limpopo power station, adding to delays.
ANC spokesman Jackson Mthembu declined to comment about the deal.