Former Catalan president Artur Mas was banned on Monday from holding office for two years for organising an illegal 2014 independence referendum.
The 61-year-old, who was Catalan leader from 2010 until last year, was convicted of civil disobedience for organising the symbolic, non-binding poll in the wealthy northeastern region in defiance of a a ban by Spain's Constitutional Court.
Catalonia, a region with its own language and customs, has long demanded greater autonomy and separatists have for years tried to win approval from Madrid for an independence vote.
Spain's economic downturn has boosted the demands, with many Catalans resenting the taxes they pay to the central government in Madrid to subsidise poorer regions.
In addition to the ban from public office, Catalonia's court of appeal also fined Mas 36,500 euros ($39,000).
Two former members of his government were also found guilty and banned from public office for 18 and 21 months.
Mas said he would appeal against the conviction in the Supreme Court.
"In the Spanish state, people are hounded for their ideas," Mas said, vowing to take the case to the European Court of Human Rights if necessary.
Spanish Prime Minister Mariano Rajoy of the conservative Popular Party said he welcomed the fact that "impunity" had not won out.
The trial stoked pro-independence fervour in Catalonia, at a time of high tensions between the local separatist government and Madrid.
- 'Disgraceful, undemocratic' verdict' -
At the opening of the trial last month, some 40,000 people massed outside the court, chanting independence slogans and waving separatist red, yellow and blue flags.
The pro-independence ERC party reacted swiftly to the verdict, slamming it as "disgraceful" and "undemocratic".
The Catalan government is committed to holding a new referendum with or without Madrid's permission by September, although the region's top legal body ruled earlier this month that only the Spanish state had the authority to call such a vote.
Anti-independence parties had asked for a legal opinion on the region's 2017 budget, which includes provisions for a referendum promised by Catalan president Carles Puigdemont.
In the November 2014 vote called by Mas, more than 80 percent of those who cast a ballot chose independence, but just 2.3 million out of 6.3 million eligible voters took part.
Calls for outright independence have increased in recent years.
Opinion polls show that Catalonia, which accounts for almost a fifth of Spain's economic output, is roughly split in half over breaking away.
Separatists say the Constitutional Court's ban on the referendum amounted to an infringement of their rights, particularly the right to freedom of expression.
They point to the example of Scotland, which held a referendum on leaving the United Kingdom in 2014.
Scots rejected independence by 55 percent to 45, but the verdict against Mas came as Scotland's First Minister Nicola Sturgeon said she would seek a new vote on independence.
Sturgeon and her pro-independence followers say the question should be asked again in the context of Brexit, since Scotland voted for Britain to remain in the EU by 62 percent in the June 2016 referendum.