Despite having his bail varied to attend the event in Canberra on Tuesday evening, Sydney's Downing Centre Local Court was told the former special forces soldier did not end up travelling to the ACT.
"Mr Roberts-Smith felt ill in the last couple days and hasn't travelled to Canberra today to attend the official opening at the war memorial," defence lawyer Slade Howell said.
The Victoria Cross recipient, who faces five counts of war crime murder, was going to attend the official opening of Anzac Hall and the memorial's atrium, displaying Australia's commitments to the Middle East, Afghanistan and peacekeeping operations.
All living recipients of Australia's highest military honour have been invited.
Defence Minister Richard Marles earlier said it was appropriate for the Afghanistan veteran to be there.
"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 be among those at the opening.
Senator Hanson had said she was hoping to speak with Roberts-Smith during the event and that he was welcome to attend given he wasn't yet 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."
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 strongly 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 at the opening.
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."
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.
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 square metres.
More than $550 million has been spent on the redevelopment.
The memorial has consistently defended displaying an image of Roberts-Smith, from which the body of a dead man has been cropped out.
A plaque under the image has been adjusted several times to reflect Roberts-Smith's arrest and previous civil court cases.
9°C