Assange was indicted by US prosecutors on 17 counts under the Espionage Act and one count under the Computer Fraud and Abuse Act in relation to WikiLeaks publication of classified material, including the Iraq War logs — with a maximum sentence of 175 years’ imprisonment.

For the past five years, Assange has been detained in HMP Belmarsh while fighting his extradition to the US in the UK courts.

He has been repeatedly refused bail on the basis that he is a flight risk because he previously attempted to flee to Ecuador when sought by Swedish prosecutors in relation to rape and sexual assault charges which were later dropped.

The plea deal is expected to be finalised tomorrow in federal court in the Mariana Islands, a US commonwealth in the Western Pacific. Assange will enter a guilty plea deal but will not be imprisoned, with his five years in Belmarsh considered time served.

Assange is expected to return to his native Australia following his release.

Michelle Stanistreet, general secretary of the National Union of Journalists (NUJ), said: “The release of Julian Assange, after a hard-fought campaign by journalists worldwide, signifies the final stages of an ordeal he has faced for several years.

“This plea deal is a hopeful beacon for Assange and his family in a case the NUJ has condemned from the start, for its wide-ranging ramifications for journalists exposing truths through their reporting.

“The targeting and persecution of journalists in this way is one that underscores the need to defend journalism and the methods used daily, including when cultivating a source.

“Collectively, we must do all that is necessary to protect press freedom and continue to resist efforts threatening the safety of journalists. As the NUJ continues to monitor developments, I hope this juncture leads to a more concrete end to the nightmare experienced by Assange.”

Jodie Ginsberg, CEO of the US-based Committee to Protect Journalists (CPJ), said: “Julian Assange faced a prosecution that had grave implications for journalists and press freedom worldwide.

“While we welcome the end of his detention, the US’s pursuit of Assange has set a harmful legal precedent by opening the way for journalists to be tried under the Espionage Act if they receive classified material from whistleblowers. This should never have been the case.”