AGL chief executive Andy Vesey has resigned from the energy company after a controversial four years in the role marked by a tense relationship with Canberra over energy policy.

Mr Vesey will be temporarily replaced by AGL chief financial officer Brett Redman while a domestic and international search for a permanent replacement gets underway.

The sudden exit comes after the company rejected earlier speculation that Mr Vesey would quit or retire after delivering AGL's full year results.

Mr Vesey has been in a standoff with the Federal Government over AGL's planned closure of its Liddell coal-fired power station in the New South Wales Hunter Valley in 2022.

Mr Vesey and the AGL board have refused Federal Government requests to extend Liddell's operation beyond 2022 or to considering selling it, which AGL has seen as unusual market intervention.

In May, AGL turned down a $250 million offer for its ageing Liddell coal-fired energy plant from Chinese-owned Alinta Energy.

Despite Mr Vesey's sudden exit, AGL chairman Graeme Hunt said in a statement that "succession planning for the CEO is a matter of key importance to the AGL board at all times."

"We thank Andy for his great contribution to AGL.

"At a time of considerable uncertainty in our sector, he has driven our transformation agenda to meet two key strategic imperatives: to prosper in a carbon-constrained future and build customer advocacy.

"He leaves the company in a robust financial position from which to continue to lead investment in our transitioning industry and in our long-term growth."

In a statement, Andy Vesey said it had been "an honour" to lead AGL.

"I am proud of what the AGL team has achieved during those years and I am now looking forward to observing AGL's continued success," Mr Vesey said.

Mr Vesey has also stepped down from AGL's board but will remain employed by AGL in an advisory capacity to the board until the end of the year.

AGL shares rose 0.7 per cent to $20.54 in early trade after news broke of Mr Vesey's resignation.

Earlier this month, AGL Energy reported a 28 per cent rise in its full-year underlying profit, bolstered by soaring power prices.

The ABC understands Mr Vesey will not be available for comment about his sudden resignation in light of previously announced succession planning.

Follow Peter Ryan on Twitter @peter_f_ryan.