Lawyers for Julian Assange are asking a London court to withdraw a UK warrant for his arrest, saying it has "lost its purpose".
The warrant was issued in 2012 after he allegedly breached bail conditions by seeking asylum in Ecuador's London embassy.
He had been facing extradition to Sweden to answer sex assault claims but these have since been dropped.
The Crown Prosecution Service says Mr Assange could walk free if he succeeds.
Before the start of court proceedings, Mr Assange's lawyer Gareth Pierce told reporters the warrant should have "no status" because the proceedings in Sweden had come to an end.
Earlier this month the UK government refused to grant the WikiLeaks founder diplomatic status and called on him to leave the embassy to "face justice".
The offence of failing to surrender to bail carries a maximum penalty of one year in prison.
The UK has refused to guarantee that Mr Assange will not be extradited to the US if he leaves the embassy.
In April 2017, US attorney general Jeff Sessions said arresting Julian Assange for releasing classified US information was a "priority".
A decision on the appeal is expected on 6 February.