Supporters of jailed hacker Julian Assange have called for an end to his ongoing incarceration during a rally held in Sydney's C-B-D, initially timed to coincide with Joe Biden's visit to the city.

The US president's absence due to his domestic political woes did little to dampen the spirits of the thousand-strong crowd, which was studded with members of Assange's family, political allies and entrepreneur Dick Smith.

The WikiLeaks founder's wife, Stella Assange, headlined the event on Wednesday, urging the US to end Assange's detention as he awaits extradition to face espionage charges.

In her first trip to the country of her husband's birth, Ms Assange has spread her message far and wide, addressing the National Press Club on Monday and meeting with federal parliamentarians.

Julian's brother, Gabriel Shipton, also spoke at the rally and was unperturbed by Mr Biden's absence.

"They're hearing the message loud and clear," he told AAP.

"They know there's millions of Australians who want this brought to a close."

Mr Shipton says support for Assange is building across the political spectrum and Australians understand the importance of the case for press freedom.

Other speakers included Assange's father, John Shipton, human rights lawyer Stephen Kenny and defence whistleblower David McBride.