Peter Tatchell has defended Julian Assange and insisted he published the "truth”.
The human-rights campaigner told talkRADIO's Julia Hartley-Brewer: "Julian Assange published the truth. He published information that exposed American government and military war crimes, human rights abuses and corruption. In that sense he performed a great public service.
“The American public should have had the right to know but they were denied that right."
Mr Assange was arrested at the Ecuadorian embassy in London, where he had been living for almost seven years.
The 47-year-old co-founder of Wikileaks faces up to 12 months in a British prison after he was found guilty of breaching his bail conditions, while the US charge could attract a maximum jail sentence of five years, according to the US Department of Justice.
Mr Assange sought political asylum in the Ecuadorian embassy in 2012 when he failed in his legal battle against extradition to Sweden, where he was wanted over two separate allegations - one of rape and one of molestation.
In May 2017, Sweden's top prosecutor dropped the long-running inquiry into a rape claim against Mr Assange, which he has always denied.
Prosecutors in Sweden have since confirmed that, while the investigation has not been resumed, they are looking into the case.
Mr Tatchell said that Mr Assange had always been willing to face the allegations in Sweden but feared he would eventually be extradited to the United States "to face very serious charges.”
“He is acting in the public interest because he is exposing wrongdoing by the US government and military," he said, adding that Mr Assange should not be extradited to the US.
“This case against him by the American government is an attack on the right to publish," he said.