Catalonia's regional assembly voted on Monday in favor of a resolution to split from Spain, energizing a drive towards independence and deepening a standoff with central government in Madrid.
The declaration, which pro-independence parties in the northeastern region hope will lead to it splitting from Spain altogether within 18 months, was backed by a majority in the regional parliament.
The fraught debate over Catalan secession has railroaded campaigning for national elections on December 20, away from the country's lopsided emergence from an economic crisis.
"The Catalan parliament will adopt the necessary measures to start this democratic process of massive, sustained and peaceful disconnection from the Spanish state," the resolution, in Catalan, said.
Parties favoring independence from Spain won a majority of seats in the Catalan assembly, representing one of Spain's wealthiest regions, in September.
But the Spanish constitution does not allow any region to break away and the center-right government of Prime Minister Mariano Rajoy has repeatedly dismissed the Catalan campaign out of hand.
The government would file an appeal with the Constitutional Court to ensure that Monday's resolution had "no consequences," Rajoy said. "I understand that many Spaniards have had a bellyful... of this continued attempt to delegitimize our institutions."
Polls show that opposition to Catalan independence is a vote winner across the political spectrum in the rest of Spain.
Catalan secessionists argue that they have tried to persuade the government to discuss the independence issue and have been blocked by unionist parties.
The declaration said it considered that judicial decisions "in particular those of the Constitutional Court" were not legitimate, setting the region and Madrid on a collision course.
A proxy independence vote was held one year ago and the erstwhile head of the regional government, Artur Mas, has been indicted for holding the ballot.
"What Catalan society faces now is the concept of politics as a war by other means," Raul Romeva, representing the Junts Pel Si party whose independence platform won the regional election, told parliament.
"We have a golden opportunity to design and construct a modern state which belongs to the 21st century, which is exemplary and able to defeat wrongdoing and corruption," he said.