Artur Mas is accused of civil disobedience for holding an unofficial independence referendum for the Spanish region in 2014.
Thousands of supporters filled the streets outside a Barcelona court house, as the former head of Catalonia went to trial.
Artur Mas, was governor of the eastern Spanish region when it held an independence vote without the legal backing of government in 2014.
He stands accused of civil disobedience, and prosecutors are calling for him to be banned from holding public office for ten years.
Mr Mas made no attempts to hide his involvement, admitting ‘the political initiative’ was his. The trial is being used by pro-independence supporters to galvanise their campaign.
Being barred from office would be a political hit for Mas, but he believes the case could hasten a split with Madrid. The Catalonian administration has vowed to hold another referendum later this year.