Javid told the Today program on Thursday: “He’s rightly behind bars. There's an extradition request from the US that is before the courts tomorrow (Friday) but yesterday I signed the extradition order and certified it and that will be going in front of the courts tomorrow.”
The US made a formal request for Assange's extradition last Thursday before a legal deadline expired.
Assange was arrested by British police on 11 April and removed from the Ecuador embassy in London where he was taking refuge after the South American nation offered him asylum. This was withdrawn in April and he appeared in court shortly thereafter.
But a Swedish judge shot down the chances of his being extradited to that country, rejecting a request in early June to issue an arrest order.
Soon after his arrest in London, the US sought his extradition to face charges of computer hacking and being involved in a compromise of classified information, a charge that carries a maximum sentence of five years.
Washington revealed its hand on 24 May when it hit Assange with 17 new charges under the US Espionage Act over his alleged role in leaking documents from former US intelligence analyst Chelsea Manning in 2010.
Assange is currently held in London's Belmarsh high-security prison where he was recently transferred to a medical unit due to his poor health.
On Tuesday, he was visited by his father, John Shipton, and the Chinese dissident artist Ai Weiwei, Britain's Press Association reported.
He is not expected to attend court but could take part via a video link.