The 49-year-old told the British court he didn't consent to being sent to the United States to be tried on 18 charges, which bring up to 175 years in prison.
An attorney acting on behalf of the U.S. government, James Lewis, accused Assange's lawyers of "an attack upon the president of the United States [which] ignores the institutional competencies of the agencies relevant to this case, the Constitution of the United States and the independence of its courts."
He also said the defense was inaccurately treating Assange as if he were a journalist.
Assange's attorney, Edward Fitzgerald, said the United States was pursuing his client for "ulterior political motives."
Assange was arrested in April 2019. He had been living in the Ecuadorian Embassy in London since 2012 when he sought asylum to dodge sexual assault charges in Sweden. Assange was arrested after Ecuador withdrew its offer of asylum. Ecuador's President Lenin Moreno said the country's patience for Assange had "reached its limit" after "repeated violations to international conventions and daily life."
The WikiLeaks founder was indicted on 17 new charges of violating the Espionage Act in May of last year and already faced a charge from March 2018 of conspiring to commit unlawful computer intrusion, which carried a maximum five years in prison. Assange was accused of working with former intelligence analyst Chelsea Manning to obtain and publicly release classified information. The new charges brought his total charges to 18 counts with each violation of the Espionage Act carrying a maximum 10-year sentence.