Prime Minister Anthony Albanese confirmed on Sunday the one-off holiday would take place on September 22, three days after the royal funeral in London.
Mr Albanese said he had already spoken to all premiers and chief ministers about plans for the national day of commemoration.
"They have all agreed that it's appropriate that it be a one-off national public holiday," he told ABC's Insiders program on Sunday.
It comes as Governor-General David Hurley prepares to mark King Charles III's accession to the throne.
Mr Albanese will recommend the governor-general proclaim Charles as the new monarch at a meeting of the Executive Council at Government House at 11am on Sunday.
The governor-general will then make the proclamation at midday outside Parliament House.
The ceremony will include a welcome to country, followed by the proclamation with God Save The King to be performed and then a 21-gun salute.
Flags that have been flying at half mast will return to full mast until dusk.
State governors will make their own proclamations in ceremonies around the country after the federal event.
The prime minister and Mr Hurley will travel to London on Thursday to attend the funeral at Westminster Abbey.
Before then, the Queen's coffin will be driven from Balmoral Castle to Scotland's capital Edinburgh and be flown to London later in the week.
It will remain at Buckingham Palace before being taken to Westminster Hall to lie in state for four days, allowing the public to pay their respects.
Mr Albanese said assistance has been given to 10 Pacific island nations that have connections with the Commonwealth to travel to London for the funeral.
Federal parliament, which was due to sit this week in Canberra, has been suspended following the death of the Queen.
The prime minister said the government would look to make up the days following the period of mourning.
"One of the days will be devoted to people being able to give their condolences on the passing of Queen Elizabeth," he said.
Meanwhile, Australians have continued to publicly mourn the monarch over the weekend.
Sandra Alexandridis, of Reservoir, burst into tears at Melbourne's makeshift memorial outside Government House while remembering the Queen on Saturday.
"She was a rock of society ... it's like you've lost your grandmother," she told AAP.
Warren Fairfax, 82, visited Government House in Sydney on Saturday, 65 years after receiving a Queen's Scout award at the same location.
"I wanted to come back and just pay respects to her … I just wanted to do that today," he said.
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