Ian Marchant is to step down as chief executive of SSE, Britain's second-biggest energy supplier, after more than a decade in the job.
Mr Marchant said he felt "the time is right for a change for both SSE and me". He will be succeeded in July by SSE's current deputy chief executive, Alistair Phillips-Davies.
He added: "I am sure that SSE will continue to go from strength to strength under Alistair's leadership. As for me, I am looking forward to new challenges – whatever they may be."
The FTSE 100 energy boss pocketed a pay package worth £1.2m last year, and was then revealed to have claimed a 12 per cent staff discount on his energy bill, saving his household around £140 a year.
Mr Marchant joined SSE's predecessor company, Southern Electric, in 1992 and joined the board of SSE as finance director when it was formed in 1998. He was appointed to the top job in 2002.
Mr Phillips-Davies joined Southern Electric in 1997 and the SSE board in 2002 as energy supply director. He became generation and supply director in 2010 and deputy chief executive last year.
The energy provider also said that finance director Gregor Alexander would have an expanded role, supporting the chief executive.
Lord Smith of Kelvin, chairman of SSE, said: "In every one of [Mr Marchant's] years as chief executive, SSE has delivered above-inflation increases in the dividend while making significant progress throughout its operations... With all of these achievements, and after 10 years' exemplary service as chief executive, I understand why Ian is choosing to step down." SSE's shares fell 53p to £13.82 per cent following the announcement.
Utilities analyst Guillaume Redgwell of Liberum Capital said that while Mr Marshall's departure from SSE will be a loss to the firm, the change at the top should not deflect it from the progress it has made in recent years.
"SSE has seen a transformation over the past 10 years and Ian will be a loss to both the company and the industry, where he has been an outspoken voice on a range of matters within energy policy," Mr Redgwell said. "But we believe that the new management can ensure a smooth transition and is well-placed to move the company forwards."