All living Victoria Cross recipients have been invited to the official opening of the memorial's atrium and Anzac Hall, a gallery focusing mainly on Australia's commitments to the Middle East, Afghanistan and peacekeeping operations.
Despite a looming trial for five counts of the war crime of murder, Roberts-Smith has successfully had his bail varied to attend the event on Tuesday evening.
It was appropriate for the Afghanistan veteran to be there as a recipient of Australia's highest military honour, Defence Minister Richard Marles said.
"The Victoria Cross recipients have been invited to this, which is appropriate. I'm comfortable about that," he told ABC TV on Tuesday.
Prime Minister Anthony Albanese and One Nation Leader Pauline Hanson will also be among those attending the opening.
Senator Hanson said she was hoping to speak with Roberts-Smith during the event and said he was welcome to attend as he hadn't been convicted of a crime.
"He's still innocent til he's been proven guilty," she told reporters in Canberra.
"I'm hoping to actually catch up with him, say hello to him, give him my support," Senator Hanson said.
The decorated soldier is accused of murdering or ordering the murders of five unarmed detainees while deployed in Afghanistan between 2009 and 2012.
After the successful bail hearing earlier in June, Roberts-Smith told reporters outside it was "absolutely" appropriate he attend the opening as a Victoria Cross recipient.
He has categorically rejected the war crime allegations and has vowed to fight them in court.
Veterans who have spoken out against Roberts-Smith, including several who he is not allowed to speak to under strict bail conditions, are also expected to attend.
Mr Albanese will tell those gathered they are bonded by the power of "lest we forget."
"That most unadorned of sentences that dwells within us like a heartbeat - we vow to keep the flame of memory burning so brightly that its glow reaches future generations," he will say in a speech.
"Today we adjourned the parliament so that everyone who wished to could come mark the opening of this Atrium and Anzac Hall, an addition to the Australian War Memorial that makes that flame burns so much brighter.
"What a sublime and powerful addition it is. A bold vision turned into a reality that enhances the institution of which it is now part."
The prime minister will implore those gathered at the event to "read all the words" about those who have gone before them.
"Look at the faces and get lost amid the smiles, the hope and camaraderie - the counterpoint to war's relentless, inhuman arithmetic. They are its true cost," he will say.
"Yet, amid this loss and sacrifice, what pulses so powerfully is life, and an abiding sense of what is worth fighting for."
Anzac Hall and the memorial's revamp will add more than 5000 square metres of gallery space - almost a full football pitch's worth - when completed in 2028, totalling 15,000 sq m.
More than $550 million in federal funding has underpinned the redevelopment.
The institution has consistently defended displaying an image of Roberts-Smith, from which the body of a dead man has been cropped out.
The picture of Roberts-Smith shows him standing in a field in Tizak in the Kandahar Province of Afghanistan.
A plaque under the image has been adjusted several times to reflect Roberts-Smith's arrest and previous civil court cases.
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