Genesis Energy's chief customer officer, Tracey Hickman, will fill in as chief executive of the power generator and retailer until a replacement for outgoing CEO Marc England is appointed.
Hickman will be interim CEO, effective from October 15.
England, who joined in 2016, informed the board a fortnight ago that he planned to leave later in the year.
The board acknowledged in a statement the "significant value" England had brought to Genesis over the past six years.