Senior Cabinet minister and long-serving Liberal Christopher Pyne is expected to retire at the next election.

Key points: Christopher Pyne to quit federal politics after 26 years as South Australian Liberal MP

Christopher Pyne to quit federal politics after 26 years as South Australian Liberal MP The Defence Minister has been a Cabinet minister since 2013

The Defence Minister has been a Cabinet minister since 2013 It follows a string of ministers to announce their retirements

The 51-year-old South Australian MP has spent half his life in federal politics and been a senior figure within the party for the last decade.

Multiple well placed sources have told the ABC the Defence Minister will announce his retirement on Saturday.

He dismissed speculation but refused to rule out an impending retirement when asked about it on Sky News on Friday.

The ABC has contacted Mr Pyne for comment.

Christopher Pyne getting ready for Question Time in the House of Representatives. ( ABC News: Matt Roberts )

Pyne's political career Elected Member for Sturt aged 25 in 1993

Elected Member for Sturt aged 25 in 1993 Became Minister for Ageing in 2007

Became Minister for Ageing in 2007 Lost deputy leader vote against Julie Bishop

Lost deputy leader vote against Julie Bishop Promoted to shadow cabinet in 2008

Promoted to shadow cabinet in 2008 Became Leader of the House in 2013

Became Leader of the House in 2013 Held defence, education and industry portfolios

He joins a string of senior Liberals to announce their retirement ahead of the federal election.

He follows ministers Kelly O'Dwyer, Michael Keenan, Nigel Scullion in leaving politics. Steve Ciobo is expected to also announce his retirement on Saturday.

Former deputy leader and current backbencher, Julie Bishop, will also retire at the election.

The looming departures come after the Parliament's biggest scalp, former prime minister Malcolm Turnbull, who has already quit politics.

Speculation had been mounting in recent weeks that Mr Pyne was reassessing his future despite repeatedly insisting he would recontest his seat.

Christopher Pyne has served as the Coalition's chief negotiator with the Lower House crossbench. ( ABC News: Toby Hunt )

The senior Liberal leader has been one of the Government's most high-profile figures, thanks in part to weekly appearances with Labor's Anthony Albanese on Channel Nine's Today Show.

He proved a viral hit following an interview on Sky News, in which he proudly and repeatedly dubbed himself a "fixer".

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Mr Pyne first entered politics aged 25, winning the eastern Adelaide seat of Sturt in 1993.

"Politics and the things that governments do affect all our lives," he told the Parliament in his maiden speech.

"The contribution that politicians can make to society is vastly underestimated and their worth is undervalued."

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Mr Pyne comfortably gained re-election in seven of the eight votes he contested in the years since.

He faced his biggest political scare in 2007, as Labor swept to power after 11 years of Coalition government.

In that election, Mr Pyne retained his seat with 50.9 per cent of the two-candidate preferred vote count.

He currently holds his seat with a 5.4 per cent margin.

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Pyne spent 14 years in the Federal Parliament before he became a minister.

Speaking in 2012 about his time in John Howard's government, he told the ABC's Kitchen Cabinet he was "an after thought" when he became the last minister appointed before the Coalition lost power.

Just days after the 2007 election Mr Pyne, who had been keen for former treasurer Peter Costello to replace Mr Howard as Liberal leader, told the ABC the former Liberal prime minster stayed in the top job for too long.

"No Liberal candidate could look in the mirror and say the leadership of John Howard was not the central factor [in the election result]," he said.

Mr Pyne ran for the Liberal Party's deputy leadership following the 2007 election, losing to Ms Bishop, who retained the role for 11 years.

Julie Bishop defeated Christopher Pyne in a Liberal deputy leadership ballot in 2007. ( ABC News: Nick Haggarty )

Under Brendan Nelson's leadership, he took on the justice and border protection portfolio before entering shadow cabinet when Mr Turnbull became Opposition Leader in 2008.

Mr Turnbull also promoted Mr Pyne to the role of manager of Opposition business over Tony Abbott, who had that role in government.

"In a choice between macho and mincing I would have gone for macho myself," then deputy prime minister Julia Gillard told the Parliament at the time.

"The leader of the Opposition faced with the choice of a doberman or the poodle has gone for the poodle."

He has served in Cabinet since the Coalition won government in 2013 and has been the chief negotiator with Labor and the crossbench in the Lower House.

Mr Pyne was education minister in Mr Abbott's government and was widely tipped to become defence minister when Mr Turnbull became prime minister in 2015.

He ultimately received that job when Scott Morrison replaced Mr Turnbull as Liberal leader in 2018.

Mr Pyne and Labor's Tony Burke approach Speaker Tony Smith as he presides over the House of Representatives. ( ABC News: Matt Roberts )

Mr Pyne remained a loyal lieutenant to Mr Turnbull when his prime ministership came under threat from Home Affairs Minister Peter Dutton's ultimately unsuccessful bid for the Liberal leadership.

He ran Mr Turnbull's numbers and reassured nervous backbenchers in a bid to keep the existing leaders in place.

The week-long leadership tumult highlighted the tensions between the conservative and moderate factions within the party.

Mr Pyne has long been a leader among the Liberal moderates and lashed out at the conservative plotters in the aftermath of the leadership change.

Mr Pyne speaks with crossbench MPs amid fears the Government was at risk of losing a vote. ( ABC News: Ian Cutmore )

"They have to be responsible for their actions," Mr Pyne said.

"They made a decision about not supporting Malcolm and they have to be responsible for that."

That leadership challenge would cost the Government its majority and not only lead to the end of Mr Turnbull's career, but ultimately Ms Bishop's and now Mr Pyne, who many had expected, given his age, would remain in federal politics for many years to come.