Julian Assange's father says his son is the subject of "vindictive revenge" from the countries he has worked to expose, and has called for the Australian government to be courageous and fight to bring the WikiLeaks founder home.

John Shipton, Assange's biological father, addressed a small group of protesters in driving rain at Sydney's Martin Place on Friday, two days after his son was sentenced to almost a year in prison for skipping bail in London.

Mr Shipton said his son was being punished for exposing the "grand narrative of every heinous crime of the late 20th century".

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"The consequence of WikiLeaks revealing these crimes, the destruction of Iraq, the destruction of Afghanistan, the destruction of Syria, the destruction of Libya, millions killed, they want their vindictive revenge," Mr Shipton told the sodden crowd of less than 50.

AAP

"Part of this resentment against Julian revealing these crimes is manifested by the English magistrate judiciary."

Mr Assange was sentenced on Wednesday to 50 weeks prison for breaching bail seven years ago, when he took refuge in the Ecuadorian embassy in London.

AAP

He was carried out of that embassy in April after Ecuador's President Lenin Moreno withdrew his country's asylum offer, describing Assange as a "spoiled brat".

The 47-year-old is formally contesting an American extradition request over a charge of conspiring to commit computer intrusion with former US Army intelligence analyst Chelsea Manning in 2010.

Assange told Westminster Magistrates Court on Thursday he did not wish to surrender himself to extradition for doing journalism that had "won many, many awards and protected many people".

He also appealed for Australian diplomatic protection.

Mr Shipton described his son's jailing as "an outrage" and said more needed to be done to bring him home.

"Australia, we (must) work together to bring Julian home to his family, to his children and to give the Australian government the courage to stop assisting this by doing nothing."