Former elite soldier Andrew Hastie has used his first major speech to outline how he will use skills developed leading men in combat against Islamic extremists to protect and represent people in the federal seat of Canning in Western Australia.

Mr Hastie, a former member of the SASR (Special Air Service Regiment) and the Liberal Party's candidate for the upcoming by-election in Canning, was speaking at the party's state conference in Perth on this weekend.

Mr Hastie also called on the Australian Defence Force (ADF) to move swiftly to conclude a long-running investigation into the alleged mistreatment of dead Taliban fighters in Afghanistan, after a media report identified him as the commanding officer of soldiers involved in such behaviour.

He drew heavily on his military experience and background, vowing to place the needs of Canning constituents as his top priority.

"I have now left the Defence Force with a clean slate, having defended our nation at the Taliban and Desh. I'm now taking the skills I learned in the Army and if elected will use them," he said.

"I've put my life on the line for that country. I've led under pressure and worked with honour, compassion and diligence. I have the strength of character to stand up for who and what I believe in."

Prime Minister Tony Abbott addressed the conference, reminding the party faithful his government "came to the rescue" of West Australians with an extra $500 million to make up the GST shortfall.

Mr Abbott received applause when he spoke about putting same sex marriage to a vote of the people.

Foreign Minister Julie Bishop spoke at the conference, talking up the Federal Government's achievements on the economy and national security.

The Canning by-election, which will be held on September 19, was triggered by the sudden death of popular local Liberal member Don Randall, who held the seat with a margin of almost 12 per cent.

Prime Minister Tony Abbott paid tribute to the former Member for Canning, the late Don Randall, whose unexpected death triggered the by-election.

He described Mr Randall as an extraordinary man.

Prime Minister Tony Abbott addresses the Liberal Party state conference in Perth. ( ABC News: Robbie Koenig Luck )

"He was a character. He was unique. He was aggravating. But by God, he was lovable. He was much loved in this room. He was much loved by his people," Mr Abbott said.

He welcomed Mr Hastie as Mr Randall's potential successor.

"He's fought for our country in the field and he'll fight for our country in the Parliament," he said.

"Thank you, Andrew, for making yourself available for this important form of national service."

Mr Hastie said Mr Randall's personal support was a testament to his charisma, drive and personal connection with the people in the electorate.

He said those same people would be his priority.

"And Prime Minister, please know that while I support our Liberal Government, the women and men of Canning will be my first priority."

After resigning his commission in the ADF, Captain Hastie is now moving from Defence Housing into the electorate, taking up residence in the suburb of Mandurah.

Hastie calls on ADF to expedite Afghanistan investigation

In his address, Mr Hastie directly confronted media reports that he was the commanding officer of a troop of soldiers investigated after amputating the hands of Taliban fighters to use for identification.

He confirmed that he had not been at the scene at the time, but was instead in a helicopter overhead.

Once he became aware of the incident, he referred up his chain of command, and it was subsequently investigated.

He said all but one soldier had been cleared, but said for the remaining serviceman the investigation was still continuing more than two years later.

Mr Hastie called on the ADF to expedite the investigation to resolve the matter.

"The least we can do for that honourable soldier is ensure that the investigation into the incident is done fully and quickly," he said.

"This issue has cast a shadow for almost two and half years over this man's life, and I believe the Defence Force has a duty of care to finalise its investigation more quickly."

Mr Hastie said his experience leading soldiers was relevant to representing the people of Canning.

He said commanding soldiers in combat was as much about caring for the men and their families, as it was selecting targets and shooting "bad guys".

"I have the experience and the training to deliver for the families and businesses of Canning," he said.

Liberals could face large swing in Canning

The 6,178-square-kilometre Canning electorate is in Perth's south-east.

The challenge for candidates will be to cut through to diverse voters ranging from fly-in, fly-out miners, treechangers in the Perth Hills, seachangers in Mandurah, farmers and semi-rural residents and a large proportion of unemployed or low-income earners.

A Newspoll survey revealed Mr Randall's 11.8 per cent margin would be wiped away and the seat left on a knife edge if the poll were held this week.

There would have been more than a 10 per cent swing, which would leave the Liberal's with a 51 per cent to 49 per cent two-party preferred lead over Labor.

Clive Palmer's Palmer United Party is also fielding a candidate for Canning, Vimal Sharma, who is the managing director at Mr Palmer's Mineralogy resources company.

Mr Palmer said he would be campaigning to save the jobs of fly-in, fly-out workers in the electorate.

"I think what matters most to me in Canning is making sure that the people who are fly-in, fly-out workers from Canning, in the Pilbara, keep their job," he said.

The Greens have not yet revealed who will be their preferred candidate in the seat.