The anti-secrecy website was lauded at the annual Walkley Awards, where winners are chosen by an independent panel of journalists and photographers, for its courageous reporting of secret US cables.
"WikiLeaks applied new technology to penetrate the inner workings of government to reveal an avalanche of inconvenient truths in a global publishing coup," the Walkley trustees said in bestowing the award Sunday evening.
"Its revelations, from the way the war on terror was being waged, to diplomatic bastardry, high-level horse-trading and the interference in the domestic affairs of nations, have had an undeniable impact."
The whistleblowing website has published thousands of cables in which US diplomats give their often candid views on world leaders, to Washington's acute embarrassment.
Assange, an Australian citizen who has previously blasted Canberra for not doing enough to protect him in the fallout from the leaks, was scathing of the government in accepting the accolade in a pre-recorded video message.
"The Gillard government has shown its true colours in relation to how it’s handled US pressure on WikiLeaks," he said in footage shown on SBS television which broadcast the awards. "Australian journalists are courageous, the Australian population is supportive, but Julia Gillard is a cowardly Australian prime minister.
"As Australians we shall not despair, as long as we can speak out, as long as we can publish, and as long as the Internet remains free, we will continue to fight back, armed with the truth," he added.
Assange has spent much of the last year under virtual house arrest in Britain since he was detained in December 2010 over claims of rape and sexual assault made by two women in Sweden.
He has strongly denied the allegations against him, claiming they are politically motivated and linked to the activities of WikiLeaks. The former computer hacker is currently appealing a decision against his extradition to Sweden to face the charges.