Oriol Junqueras, the Catalan regional government's former deputy leader, said in emailed answers to questions that the prison sentences imposed on him and eight others on charges of sedition only made them and their movement stronger and more determined.
The court on Monday slapped the longest prison term, 13 years, on Junqueras. The convictions sparked protests across the region.
"What I'm sure of is that this conflict is to be resolved via ballot boxes ... we are convinced that sooner or later a referendum is inevitable because otherwise, how can we give a voice to the citizens?" he wrote from prison, adding that he did not regret having organised a referendum in 2017.
In his first interview after the sentence, Junqueras told Reuters that he and others planned to appeal the sentences with the European Court of Human Rights in Strasbourg. When asked what message he would give to the independence movement after the sentencing, Junqueras said:
"That we will carry on and not give up because we never have and won't do it now. That prison and exile have made us stronger and makes us ever more convinced, if that is possible, in our profoundly democratic beliefs."
Junqueras' responses were transmitted to Reuters by his staff late on Monday.
All defendants were acquitted of the gravest charge, rebellion. Three other defendants were found guilty only of disobedience and not sentenced to prison.
"I'm sure this sentence will not weaken the independence movement, quite the contrary," he said.Catalonia's independence drive has been a major challenge for Spain for years, attracting worldwide attention when separatist leaders defied courts and conducted a referendum on secession in October 2017 and a subsequent short-lived declaration of independence.