The trial has further strained relations between pro-independence political parties in Catalonia and Spain's central government as a long-running battle over the region's attempts to hold a referendum on secession reaches a tipping point.
The former head of Spain's Catalonia region is barred from public office for two years for staging an informal referendum on independence in 2014 at a time when secessionist leaders are trying to drum up support for a new ballot; the ruling came down on Monday
Artur Mas - who was regional governor in 2014 when pro-independence campaigners held a symbolic referendum in breach of a legal order - was found guilty of contempt of court, Catalonia's Superior Court of Justice said in a ruling.
"We would do the same thing as we are democrats and we are obliged, as democrats, to listen to the people and obey their mandate at the polls ... We will appeal in Spain and then take the case to European courts, if we need to," Mas said during a conference after the ruling.
Leaders in Catalonia, a wealthy region with its own language and distinct culture, have vowed to move ahead with another referendum on secession in September in spite of opposition from Spain's centre-right Prime Minister Mariano Rajoy.
Separatist parties, which hold a majority in the local Catalan assembly, rallied behind Mas during his trial, and the court case galvanised pro-independence supporters.
"A mistake! What a difference compared to consolidated and healthy democracies," current regional head Carles Puigdemont said via Twitter following the announcement and the news of calls for a second referendum in Scotland.
Scotland's First Minister Nicola Sturgeon's demand on Monday to hold a new Scottish independence referendum in late 2018 or early 2019, once the terms of Britain's exit from the European Union are clearer, may help embolden Catalan campaigners.
Spain's Rajoy has repeatedly ruled out giving the region a vote on independence, saying it would be illegal and against the constitution - a stance supported by the judiciary.
The last referendum, held in November 2014, was deemed illegal by Spain's Constitutional Court, and the ballot was manned by volunteers and grassroots campaigners to get around the restrictions.
Mas, who stepped down as leader in early 2016, was accused of disobedience against the state for still allowing the symbolic vote to go-ahead. Two other former officials from his administration were also found guilty on Monday.
The 2014 ballot drew a turnout of about 2.2 million out of a potential 5.4 million voters, with a strong showing from pro-independence supporters. More than 80 percent of voters backed splitting from Spain.