Mashego joined Harmony in 2005 in the human resources discipline. He has since been responsible for a variety of portfolios at senior management level and as an executive. These include general manager at Evander, human resources executive and government and stakeholder relations. Mashego was appointed an executive director corporate affairs on 24 February 2010. He represents Harmony on a number of boards as a director including the Mining Qualifications Authority (MQA), Enactus where he is the deputy chairman of the board, and the Rand Refinery where he is also the chairman of the social and ethics committee, as well as a number of Harmony Gold subsidiaries. Mashego received the United Nations Global Leadership Award, together with an honorary doctorate in philosophy in March 2023.