Governor-General Sir Peter Cosgrove will retire when his five-year term finishes next year, saying the job “deserves and demands new vigour”.

Former deputy Liberal leader Julie Bishop has been touted as a possible replacement for Sir Peter, if she was to quit parliament.

Labor leader Bill Shorten has already called on the government to extend Sir Peter’s tenure, but the former defence force chief says he will step down at the end of March.

“That’s when my five years is up. It’s not fixed, but if you do the job properly, at the end of five years you’re probably running out of puff a bit … after five years, the job deserves and demands new vigour,” he told The Australian on Wednesday.

If Sir Peter steps down in March, his replacement is likely to be chosen by Prime Minister Scott Morrison – ahead of the federal election that must be held by May 2019.

But last week, amid rumours that Ms Bishop was a possible contender, Mr Shorten wrote to Mr Morrison asking him to extend Sir Peter’s term for six months.

That would give Mr Shorten a chance to pick the new governor-general if Labor wins the election.

Governor General Julie Bishop? Not so fast warns @billshortenmp who has written to new PM @ScottMorrisonMP warning current GG term should be extended so Libs don’t get to appoint new one – should be whoever wins next election pic.twitter.com/wVQTgvWIjN

— Samantha Maiden (@samanthamaiden) August 27, 2018

“Such an extension is within convention and would be supported by the Opposition,” Mr Shorten wrote.

Sir Peter told The Australian he intended to live a quiet life in retirement.

“You very much, when you retire, you take, in a profile sense, a back seat,” he reportedly said. “You don’t want an immediate past governor-general turning up and making a pro­nounce­ment or something.

“You can still get involved in plenty of worthy projects in the community, in a less-noticed way. You try not to be on the front pages.”

Sir Peter was sworn in as Governor-General in March 2014. He was previously Australia’s Chief of Army from 2000-2002, and Chief of the Defence Force from 2002-2005.

He also led the taskforce helping to rebuild communities in Queensland after Cyclone Larry in 2006.

-with agencies