Origin Energy has replaced veteran chief executive Grant King with his long time offsider Frank Calabria.

Mr King has been Origin’s only leader since it was spun out of gas giant Boral in 2000.

Mr Calabria joined Origin in 2001 as chief financial officer, but has more recently served as head of the company's energy markets division.

Calabria’s division is at the centre of Origin's business activities, overseeing the generation and sale of electricity and gas to around 4.2 million domestic customers.

Mr Calabria will take on an ongoing debt reduction program and oversee the completion of the $24.5 billion APLNG project in Gladstone as well, in which Origin holds a 37.5 per cent stake.

Origin chair Gordon Cairns says the company enjoyed a prolonged period of growth under Mr King.

“The past year has been a transitional one for Origin with good progress being made in debt reduction following last year's fall in oil prices,” Mr Cairns said.

“The company's focus in the short term remains on accelerating debt reduction and improving returns.”

Mr Calabria says he is there to cut debt and improve performance.

“This twin focus will improve returns for shareholders and position us to drive medium term growth in a rapidly changing energy market, while delivering on the major potential for the major investment that has been made in APLNG,” Mr Calabria said.