Six members of the Parliament have undertaken a trip to Washington DC to lobby for the charges against Assange to be dropped.

The six are former Nationals leader Barnaby Joyce, Liberal Senator Alex Antic, Labor MP Tony Zappia, Independent MP Monique Ryan and Greens Senators David Shoebridge and Peter Whish-Wilson.

Assange is still being held in the UK's Belmarsh maximum security jail as he awaits the outcome of a second appeal to the UK High Court against an extradition order.

The second appeal was filed on 13 June. Since then his wife, father and brother have been campaigning for his release.

The 63 parliamentarians, who call themselves the Bring Julian Assange Home Parliamentary Group and are from across the political spectrum, said in the letter: "As Australian Parliamentarians, in support of our colleagues’ delegation to the United States in September 2023, we are resolutely of the view that the prosecution and incarceration of the Australian citizen Julian Assange must end.

"Together with a large and growing number of Australians, we believe it is wrong in principle for Mr Assange to be pursued under the Espionage Act (1917), and that it was a political decision to bring the prosecution in the first place."

They said the detention of Assange "serves no purpose, it is unjust, and we say clearly — as friends should always be honest with friends — that the prolonged pursuit of Mr Assange wears away at the substantial foundation of regard and respect that Australians have for the justice system of the US".

"We agree entirely with the position expressed by the Australian Prime Minister Anthony Albanese who said in the House of Representatives on 22 May 2023 that 'enough is enough when it comes to the ongoing incarceration of Julian Assange and that nothing is served from the ongoing incarceration of Julian Assange'.

"We welcome the recently expressed agreement on this point from the Leader of the Opposition, [Peter Dutton], and we make clear that the bipartisan leadership support for this position is matched by the wide cross-party and independent support within the Australian Parliament itself, which in turn reflects the strongly held views of the Australian community."

The letter said the members of parliament were grateful for the support in the US for an end to the legal pursuit of Assange from members of Congress, human rights advocates, academics, and civil society, and from within the US media in defence of free speech and independent journalism.

"On that basis we ask Congresspeople, members of the press, and other relevant civil society stakeholders in the US to speak up now in supporting an end to the prosecution and detention of Julian Assange."

Assange was arrested by British police on 11 April 2019 and removed from the Ecuador embassy where he had taken refuge. His asylum was withdrawn shortly before he was arrested and he appeared in court soon after. The US made a formal request for his extradition on 6 June 2019.

The Australian, 52, is one of the better known hackers Australia has produced.