Twelve politic, pro-independence activists and cultural leaders were being tried for their involvement in the referendum, reports Efe news.
Vice President of the Catalan Parliament Oriol Junqueras was sentenced to 13 years prison for sedition and misuse of public funds, while politic Raul Romeva, Dolors Bassa and activist Jordi Turull have all been handed a 12-year sentence.
Three other defendants were found guilty of disobedience and fined, but will not serve prison sentences, the BBC said.
The 12 politic and activists have denied the charges.
The prosecution had sought up to 25 years in prison for Junqueras, who is also the highest-ranking pro-independence leader on trial.
He was handed the longest sentence of 13 years among the 12 accused.
Some of the leaders, speaking to the BBC ahead of the trial, said the proceedings were political in nature.
Any violence, they said, was on the part of police and committed against voters in a crackdown which made headlines around the world.
Following the verdict which came after four months of hearings, Catalan independence supporters marched in Barcelona displaying banners that read "free political prisoners" while urging others to "take to the streets".
Over the weekend, hundreds of protesters rallied in the city.
In 2017, police and protesters clashed when Catalonia's pro-independence leaders went ahead with a referendum ruled illegal by Spain's constitutional court.
Three weeks after the banned 2017 vote, the Catalan parliament declared an independent republic. Madrid stepped in to impose its rule on the region, and several Catalan leaders fled or were arrested.
Carles Puigdemont, the former Catalan President, escaped trial after fleeing Spain in October 2017 before he could be arrested, along with four others.
The wealthy Catalan region is home to about 7.5 million people, with their own language, parliament, flag and also an anthem.
In September, a march in Barcelona in support of Catalonia's independence from Spain drew crowds of about 600,000 people - one of the lowest turnouts in the eight-year history of the annual rally.
( With inputs from IANS )