U.S. authorities accuse Assange of scheming with former Army intelligence analyst Chelsea Manning to break a password for a government computer and leak hundreds of thousands of classified documents.
Assange’s attorney, Edward Fitzgerald, said the 48-year-old Australian is protected by a 2007 extradition treaty between Britain and the U.S.
"We say that there is in the treaty a ban on being extradited for a political offence and that these offenses as framed, and indeed in substance, are political offenses," Fitzgerald said at a court hearing.
Assange spent almost seven years holed up in the Ecuadorian Embassy in London to avoid a rape investigation in Sweden. He was arrested by British police in April after Ecuador withdrew his asylum status and jailed for jumping bail when he sought shelter inside the embassy in 2012.
Assange remains in custody at London’s Belmarsh Prison while he fights extradition. Fitzgerald said Assange’s defense team would call up to 21 witnesses at the full extradition hearing next year.
He said the evidence being submitted would cover the case of Manning, medical evidence, Assange's prison conditions and ongoing Spanish legal proceedings relating to the alleged "bugging of the conversations with his lawyers in the Ecuadorian Embassy."
Fitzgerald reiterated complaints that Assange's lawyers were having "great problems" seeing him in prison.
Assange appeared at Thursday's case management hearing by video link from prison. He spoke to confirm his name and date of birth, then sat with his head bowed, occasionally closing his eyes during the 45-minute proceedings.
The full extradition hearing is scheduled to begin Feb. 24 and could take four weeks.
Swedish authorities dropped the rape probe last month, citing the many years that have elapsed since the accusation was made over nine years ago.