The court remanded him into custody pending sentencing.
Assange faces a sentence of up to 12 months for the conviction.
He will face another court hearing on May 2 on a request made by the US for his extradition for alleged computer hacking.
According to the US Justice Department, Assange allegedly conspired in March 2010 with Chelsea Manning, a former US Army intelligence analyst, to crack a password stored on Department of Defence computers and leaked massive military and diplomatic documents.
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