Protesters blocked some roads in Barcelona, while civil servants gathered outside some government buildings. "Today they have violated all their rights. It is horrible that Europe doesn't act," 60-year-old civil servant Deni Saball said while protesting in the street. "I don't want to be European. I don't want to be Spanish."
Protests were also reported in other towns across the wealthy northeastern region. The Supreme Court sentenced nine leaders to sentences from 9-13 years for sedition and misuse of public funds. Three more were given fines but not jail time.
Former Catalan vice president Oriol Junqueras says the region's independence from Spain "is closer than ever."
After being sentenced to 13 years in prison for his role in an illegal 2017 secession attempt, Junqueras said "we Catalans do not have an alternative."
The comments were carried by his Republican Left party after the sentence by the Supreme Court was released on Monday.
Former Catalan regional president Carles Puigdemont, who fled Spain to Belgium along with several others following the failed secession bid, wrote on Twitter that he was appalled by the verdict.
"A total of 100 year of prison. How horrible. Now more than ever, we will be you and your families. For the future of our sons and daughters. For democracy. For Europe. For Catalonia," he said.
Spain's Supreme Court has convicted 12 former Catalan politicians and activists for their roles in the secession movement of 2017.
The court on Monday sentenced the former regional vice president, Oriol Junqueras, to 13 years for sedition and misuse of public funds.
The 12 were tried for their actions in a 2017 attempt by Catalonia to break away from Spain following an illegal independence referendum.
Grassroots pro-secession groups have previously said that if any of the defendants were found guilty they would organize protests and "peaceful civil disobedience."
Spanish authorities have deployed hundreds of extra police to the region in anticipation of the ruling.