Prime Minister Malcolm Turnbull has reaffirmed his support for an Australian republic but says the country will not support the change happening before Queen Elizabeth ends her reign.

Key points: Next referendum to make Australia a republic needs to be more inclusive, PM says

Next referendum to make Australia a republic needs to be more inclusive, PM says Mr Turnbull says not enough grassroots support for that referendum to pass

Mr Turnbull says not enough grassroots support for that referendum to pass For decades he has been one of the country's strongest advocates for an Australian head of state

In a speech to the Australian Republican Movement at its 25th anniversary dinner in Sydney on Saturday night, Mr Turnbull said the next referendum to make Australia a republic needs to be more inclusive and less confusing than the movement's failed bid in 1999.

"Australian people need to feel like they chose the model," he said.

"The clear lesson is that you cannot succeed in any referendum, let alone one that goes to touchstones of national identity, if the proposal is not seen and understood by the Australian people as one over which they all have ownership."

Mr Turnbull used the speech to put forward his road map on how a new referendum should be presented differently, namely that Australians first choose how the president was elected, before that model was put to them in later referendum.

"We would need to have an advisory plebiscite which offered a choice of two republican models, preferably direct election and parliamentary appointment [of the president]," he said.

Mr Turnbull doubted whether there would be any support for a president who had "different, let alone wider, powers" to the Governor General.

He also said the "cold and unyielding practical reality" is that there is currently not enough grassroots support for that referendum to pass.

"It is hard to see how this issue would return to the forefront of debate during the Queen's reign," Mr Turnbull said.

'Right now an Australian republic is not inevitable'

The Prime Minister told his audience there were a list of important constitutional issues that the Parliament had to address, including securing constitutional recognition for Indigenous Australians.

"What Parliament needs to see is a strong grassroots political movement mobilising a substantial majority behind the republic, that must be delivered by [the] republican movement today … not by the Government or the Opposition," he said.

Mr Turnbull said the timing of the next referendum is critical in order to avoid a repeat of the movement's failed bid in 1999.

"The deeper its grassroots the better-positioned it will be when its position becomes salient again, it has to be a genuine, popular movement and to proceed on any other basis is to miss what happened in the 1990's and that's what leads to failure," he said.

Mr Turnbull has for decades been one of the country's strongest advocates for an Australian head of state.

As a one-time leader of the Australian Republican Movement in the lead-up to the failed 1999 referendum, he fought a bitter public battle against monarchist spokesman Tony Abbott, who he last year later toppled as prime minister.

Mr Turnbull told the audience they had a massive task ahead of them in order to rebuild the ground support needed for another referendum bid.

"House by house, street by street, suburb by suburb — we must make the case to our fellow Australians that we deserve one of our own as head of state," he said.

"Right now an Australian republic is not inevitable, but we can make it so by working together on this great unfinished business for our nation."