Julian Assange has won a bid to bring an appeal against his extradition to the United States at the High Court in London.

Assange faces prosecution in the US over an alleged conspiracy to obtain and disclose national defence information following the publication of hundreds of thousands of leaked documents relating to the Afghanistan and Iraq wars.

During a two-day hearing in February, lawyers for the 52-year-old asked for the go-ahead to challenge a previous judge’s dismissal of his case to prevent his extradition.

Dame Victoria Sharp and Mr Justice Johnson dismissed most of Assange’s legal arguments but said that unless “satisfactory” assurances were given by the US, he would be able to bring an appeal on three grounds.

Those assurances were that Assange would be protected by and allowed to rely on the First Amendment – which protects freedom of speech in the US – that he is not “prejudiced at trial” due to his nationality, and that the death penalty is not imposed.

And at a hearing on Monday, the two judges granted permission to appeal.

This means Assange will now be able to bring an appeal at the High Court in London.

Lawyers on behalf of the US had said Assange’s bid to bring an appeal should be refused given the promises, provided in a note from the US embassy in London.

James Lewis KC said in written submissions that there is “no question” that Assange, if extradited “will be entitled to the full panoply of due process trial rights, including the right to raise, and seek to rely upon, the first amendment as a defence”.

He later told the court: “The assurance does make it clear that he will not be discriminated against because of his nationality.

“He can and will be able to raise all those arguments and his nationality will not prejudice a fair trial.”

Edward Fitzgerald KC, for Assange, said most of the promises were “blatantly inadequate” but that they had accepted the promise about the death penalty.

In written submissions, the barrister said that while the assurance over the death penalty was “an unambiguous Executive promise”, the other assurance does not give “any reliable promise as to future action”.

The barrister added: “What needs to be conclusively removed is the risk that he will be prevented from relying on the first amendment on grounds of nationality.”