The Sydney Peace Foundation has accused the federal government of "demonising" Queensland-born WikiLeaks founder Julian Assange as it handed him its highest award.

The peace foundation presented Mr Assange a gold medal in recognition of his "exceptional courage in pursuit of human rights" at a ceremony in London on Tuesday.

It is only the fourth time in the organisation's 14-year history that the prize for extraordinary achievement in promoting peace with justice has been given out.

Previous winners are Nelson Mandela, the Dalai Lama and Japanese Buddhist leader Daisaku Ikeda.

Foundation director Professor Stuart Rees said the award was to honour Mr Assange's work in challenging official secrecy.