The Australian, who has been holed up in the Ecuador embassy in London for two years to avoid extradition to Sweden, could be able to leave the building if the court rules in his favour.
In August he said we would leave "soon", amid reports that he was suffering from a heart condition and other ailments.
A European arrest warrant was issued to enable Swedish prosecutors to question Assange about accusations of rape and sexual molestation brought against him by two women in their 30s when he visited the country in 2010. Assange denies the claims.
"We will win because the law is very clear. My only hope is that the court is following the law and is not pressured politically to do anything outside of the law," Assange said via a video link screened at a human rights film festival in Barcelona.
His lawyer in Sweden Per Samuelsson refused to comment ahead of the verdict today.
Assange fears extradition to Sweden could lead to him being transferred to the United States to face trial over WikiLeaks' publication of classified US military and diplomatic documents.
In 2010, WikiLeaks began publishing 250,000 American diplomatic cables and 500,000 classified military reports, covering both American diplomacy and the US wars in Iraq and Afghanistan.
