Prosecutor Emilio Sanchez accused Mas, president of Spain's wealthy, northeastern region from 2010 to 2016, of breaking "the rules of the democratic game" and of open defiance for organising the symbolic referendum despite a ban by Spain's Constitutional Court.
Accused of serious civil disobedience and misconduct, the 61-year-old retorted he and his two co-defendants had never intended to disobey.
"But yes, there was the intention to stand up to a Spanish government that was stopping people from participating in a normal, democratic way," he said in his final plea.
The trial has stoked pro-independence fervour in Catalonia at a time of high tensions between the local separatist government and Madrid, with 40,000 supporters turning up Monday on the first day of trial.
Prosecutors want Mas and his former associates banned from holding public office for nine to 10 years.
But their defence argues they were merely defending "the right to freedom of expression" for Catalans, many of whom want a say in the future of their 7.5 million-strong region.
Catalonia, a region with its own language and customs, has long demanded greater autonomy.
But in recent years, tensions with Madrid have markedly increased, as have calls for outright independence, culminating with the election in 2015 of a pro-independence government in Catalonia backed by a majority separatist regional parliament.
When he was president, Mas had initially tried to hold a referendum similar to the one organised in Scotland in 2014, but this was banned by the court.
So he decided instead to hold the non-binding, symbolic vote for which he and his associates were on trial this week.
More than 80 percent of those who cast their ballot in the 2014 vote did so for independence - although just 2.3 million people out of a total of 6.3 million eligible voters took part.
"I'm responsible for having listened to people on the streets and in the polling booths, I'm responsible for having fulfilled parliamentary mandates... and I'm not hiding, I'm proud," Mas told the court.