Fortescue has been Electra's chief investment partner since he joined in 2011 and succeeds Hugh Mumford, who is retiring after 34 years with Electra.
Mumford will remain as chairman of Electra' investment committee, and Bill Priestley will take over Fortescue's position as chief investment partner.
Electra said the changes are part of its long term "succession plan", which started in 2010.
Fortescue was global head of retail and consumer group at Apax Partners and since joining has been involved in a number of Electra transactions, including Parkdean Resorts, Knight Square, CALA, Davies Group, AXIO and Hotter Shoes.
Priestley, who joined Electra in January 2014, led Electra’s investments in Innovia Group, The Original Bowling Company and TGI Fridays. He was previously managing director at LGV Capital.
Fortescue said: "Under Hugh's long and successful leadership Electra Partners has developed a unique style of private equity investing, becoming known for its patient, disciplined and flexible approach, which has generated compound growth on Electra Private Equity's share price of more than 14 per cent per annum over the last 23 years.
"I look forward to continuing to work with my team at Electra Partners to deliver more of the same in the future. We are very pleased to be retaining Hugh's wisdom and experience through his continued chairmanship of the investment committee."