An appeal is almost certain in a case that has attracted international attention. Assange's detractors see him as a traitor over his WikiLeaks’ publication of thousands of leaked military and diplomatic documents a decade ago. His supporters see his imprisonment as an affront against the free press.
A lower court judge refused an American request to extradite Assange to the U.S. to face spying charges. A judge said Assange, 50, who is currently being held at London’s high-security Belmarsh Prison, could kill himself if held under harsh U.S. prison conditions.
An attorney for the U.S. government who appealed the decision denied that Assange’s mental health was too fragile to withstand the U.S. judicial system and even assured the court that any sentence handed down could be carried out in an Australian prison.
The appeals will likely end up in the Supreme Court.
Stella Moris, Assange's fiancée, told reporters that his legal team would appeal the court's decision, Reuters reported.
"How can it be fair, how can it be right, how can it be possible, to extradite Julian to the very country which plotted to kill him?" she said. "We will appeal this decision at the earliest possible moment."
The Associated Press contributed to this report