The Supreme Court judges thus declined the appeal of Junqueras, who has been detained on suspicion of sedition, rebellion and misuse of state funds and remained in custody since November without a right to release on bail.
The three judges have unanimously decided that there was a "risk of repeat crime because there is no information proving that the applicant intends to refrain from committing" a crime.
The judges pointed out that it was legal to defend the independence of a certain territory, but it had to be done within a legal framework, while Junqueras was a member of the government that unilaterally declared the independence of Catalonia.
The referendum on independence was held in Catalonia on October 1, despite opposition on part of Madrid. More than 90 percent of the voters who cast their ballots backed the region's independence. The regional authorities announced independence unilaterally in late October, but Madrid then imposed direct rule over Catalonia, dissolving the government and the parliament.
Several Catalan politicians were arrested, but most of them, unlike Junqueras, were released for the duration of the pre-trial investigation.