Prime Minister Scott Morrison, speaking at the service on Monday, said Australian troops had protected Australia's democracy and passed on a democratic inheritance.

"What ultimately matters in that task is a fierce and protective love for their nation and of their liberty, a love of home, family, community and country. A willingness to live for all of these things, but if necessary, sacrifice for something far greater than ourselves," he said.

"This morning, far away from here, the people of Ukraine are doing exactly that, and on this particular day as we honour those who fall for our liberty and freedom, we stand with the people of Ukraine who do the same thing at this very moment."

Mr Morrison described the Hall of Memory at the Australian War Memorial, and its mosaic depicting the devotion of services personnel, saying that value had compelled the people who had defended the nation through history.

"Devotion to Australia, to our values, has compelled women and men in all the places, in all the battles, where our history has been written," he said.

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Deputy Labor leader Richard Marles, attending in place of Anthony Albanese while the opposition leader is stuck in COVID isolation in Sydney, also acknowledged Ukrainians fighting against Russian invading forces.

Mr Marles said Darwin was "where war first met Australia".

"In the 80 years since, Territorians have continued to know war," Mr Marles said, naming Darwin soldiers who died in service.

Mr Morrison and Mr Marles laid wreaths at the Darwin cenotaph, after the Last Post was played and the ode was recited. About 9000 people were expected to attend the service next to Darwin's harbour.

Mr Morrison met members of the public after the ceremony. He is also expected to attend the Anzac march in Darwin on Monday morning.

Mr Albanese said in a video message the Australian character was confirmed at Gallipoli and since then Australians had "stood steadfast as warriors and as builders and keepers of the peace".

"Yet as the war in Ukraine so tragically reminds us, darkness is not vanquished from the world," he said.

"It reminds us freedom cannot be taken for granted. It reminds us that freedom isn't free."