The former Catalan vice-president Oriol Junqueras has been jailed for 13 years for his part in the 2017 independence uprising there.
The Spanish Supreme Court sentenced him on Monday, Spanish state broadcaster TVE reports.
He was found guilty of sedition.
It also sentenced Jordi Sànchez, former president of the Catalan National Assembly, and Jordi Cuixart, leader of the Òmnium Cultural group, to nine years in prison.
In total, nine separatist leaders were given between nine and 13 years in prison for the charge of sedition.
Three other defendants were found guilty of disobedience and not sentenced to prison.
The former head of the Catalan parliament, Carles Puigdemont, remains in self-imposed exile in Brussels.
He was arrested on foot of a European Arrest Warrant by German authorities at the Danish border in March last year.
However a German court agreed to release him on bail.
Reacting to the sentences, he called the decision to jail the nine for a total of 100 years a "barbarity".
He tweeted: "100 years of imprisonment in total. A barbarity. Now more than ever, by your side and that of your families.
"Tap react, like never before. For the future of our sons and daughters. For democracy. In Europe. By Catalonia."
100 anys de presó en total. Una barbaritat. Ara més que mai, al vostre costat i al de les vostres famílies. Toca reaccionar, com mai. Pel futur dels nostres fills i filles. Per la democràcia. Per Europa. Per Cataunya.
— Carles Puigdemont (@KRLS) October 14, 2019
Josep Rull, Catalonia's former regional government councillor, was sentenced to 10 years and six months in prison.
He said: "If they had judged us on the facts, they would have acquitted us. Because they have judged ideas, they have condemned us.
"Condemning us, they have condemned the 2.5 million Catalans who voted on October 1 in one of the most extraordinary exercises of democracy that Europe has seen in the 21st century."
In 2017 the group attempted to break Catalonia away from Spain following an independence referendum.
The Taoiseach Leo Varadkar had warned that Ireland would not recognise the result of the October 1st Catalonian referendum.
The Spanish government declared the election illegal and unconstitutional.
Of the 2.2 million voters who were able to cast ballots in the banned referendum, two million voted for independence.
The violent response of Spanish authorities to the referendum - broadcast worldwide with images of police using rubber bullets and batons on voters - prompted discomfort internationally and fury in Catalonia.
Some 900 people were injured as police attempted to prevent people from casting their ballots.
Additional reporting: IRN
Main image: Oriol Junqueras, former vice-president of Catalan government, is seen in Barcelona in 2017 | Image: Matthias Oesterle/Zuma Press/PA Images
