"I welcome President Obama's decision to commute the sentence of Ms. Chelsea Manning from 35 years to time served," Assange said in a statement yesterday sent to AFP by one of his lawyers.
He said Manning should never have been convicted and described her as "a hero, whose bravery should have been applauded not condemned".
"In order for democracy and the rule of law to thrive, the government should immediately end this war on whistleblowers, and publishers such as WikiLeaks and myself," Assange added.
A transgender soldier, she was sentenced by military court martial as Bradley Manning and has since been held in an all-male prison, where the 29-year-old has attempted suicide twice.
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Earlier this month WikiLeaks said on Twitter that Assange would agree to US extradition if Obama were to grant Manning clemency.
He has been living in the Ecuadorian embassy in London since June 2012 to avoid being extradited to Sweden, where he faces sexual assault allegations, claiming he fears he would be extradited from there to the US over his role in the leaks.
"Julian's US lawyers have repeatedly asked the Department of Justice to clarify Julian Assange's status and would like them to do so now by announcing it is closing the investigation and pursuing no charges," lawyer Melinda Taylor, representing Assange, told AFP.
Washington has maintained the threat of prosecuting Assange over the 2010 leak, though no charges have been filed.