Victoria Cross recipient Ben Roberts-Smith will not attend the official unveiling of a new gallery at the Australian War Memorial on Tuesday because he has fallen ill. 

The nation's four surviving VC holders were invited to the Anzac Atrium and Anzac Hall, a gallery focused on Australia's commitments to the Middle East, Afghanistan and peacekeeping operations.

Roberts-Smith, who was charged in April with five counts of 'war crime-murder' allegedly committed while serving with the SAS in Afghanistan, had his bail varied to attend the event on Tuesday evening.

Defence Minister Richard Marles said it was appropriate for Australia's most decorated living soldier to be there as a recipient of the country's highest military honour.

'The Victoria Cross recipients have been invited to this, which is appropriate. I'm comfortable about that,' he told ABC News on Tuesday.

Prime Minister Anthony Albanese and One Nation Leader Pauline Hanson will be among those attending the opening but a source close to Roberts-Smith told the Daily Mail he had been forced to withdraw due to illness.

Senator Hanson said she was hoping to speak with Roberts-Smith during the event and said he was welcome to attend as he had not been convicted of a crime.

'He's still innocent until he's been proven guilty,' she told reporters in Canberra earlier on Tuesday.

'I'm hoping to actually catch up with him, say hello to him, give him my support.' 

Roberts-Smith is accused of murdering or ordering the murders of five unarmed detainees while deployed in Afghanistan between 2009 and 2012.

After his successful bail hearing earlier in June, Roberts-Smith told reporters it was 'absolutely' appropriate he attend the gallery opening as a VC recipient.

The 47-year-old, whose uniform and medals are on display at the memorial, 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.

Albanese is expected to 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 burn 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 5,000sqm of gallery space - almost a full football pitch's worth - when completed in 2028, totalling 15,000sqm.

More than $550million in federal funding has underpinned the redevelopment.

The institution has 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.