LONDON — A British court on Friday set February 2020 as the date for the full extradition hearing on whether Julian Assange, the founder of WikiLeaks, should be sent to the United States to face a slew of charges, including several under the Espionage Act.

Mr. Assange, 47, appeared by video link from Belmarsh Prison on the outskirts of London for his first hearing since the United States formally requested his extradition. He had skipped a previous hearing because, his lawyer said, he was too ill to appear. Some experts, including a United Nations official, said he had exhibited signs of a deteriorating physical and mental condition.

Mr. Assange’s hearing came days after Britain’s home secretary, Sajid Javid, signed the extradition request from the United States and expressed his support for Mr. Assange’s detention.

“He’s rightly behind bars,” Mr. Javid told BBC’s Radio 4.

Protesters holding signs that read “Hands off Assange” outside Westminster Magistrates Court in London on Friday denounced Mr. Javid’s decision and demanded Mr. Assange’s release. If the court rules in the United States’ favor, the extradition process is expected to be a long and complicated one.