Catalan lawmakers have formally approved a road map for independence from Spain by 2017.
In an historic but widely expected vote, the nation's parliament split 72 to 63 in favour of a plan that effectively seeks to override Spanish judicial blocks on creating a new state in Iberia.
The move comes after independentistes won parliamentary elections billed as a proxy independence referendum in September.
Unionists say the victory by two pro-independence slates, Junts pel Sí and the leftist CUP, was not emphatic enough to pursue a course that could end in a unilateral breakaway.
However, Raul Romeva, the left-wing politician who topped the Junts pel Sí slate in the Catalan capital Barcelona, said a "disconnection" between the two Iberian nations of Spain and Catalonia was now inevitable.
Speaking of the charge to independence, Mr Romeva said: "There is now no brake. If it doesn't happen today, it will happen tomorrow.
"If it is not us, it will be others. But that country has loudly and clearly that the time has come to just go for it."
Opening the session of parliament, Mr Romeva has said: "There is a growing cry for Catalonia to not merely be a country, but to be a state with everything that means.
"Today we don't only open a new parliament, this marks a before and after."
Spanish Prime Minister Mariano Rajoy, pictured below, has previously vowed to take legal action against the Catalan parliament if it was to approve the secession plan.
The motion passed by the parliament in its first post-election session, declared "the start of a process toward the creation of an independent Catalan state in the form of a republic" and a "process of democratic disconnection not subject to the decisions by the institutions of the Spanish state".
This is the crunch. Catalan parliamentarians have voted to ignore any legal or legalistic challenges, from either Mr Rajoy, who faces Spain-wide elections next month, or Spain's Constitutional Court.
The country's president, Artur Mas, is already facing an unprecedented criminal charge of usurping power by carrying out a mock referendum last year.
Having lost at the polls in September, Catalan branches of Spain's ruling conservative Popular Party or PP and the Socialist and the arch-unionist Ciutadans opposition parties had filed appeals to halt the road map vote in parliament, but Spain's Constitutional Court ruled last Thursday that it could go ahead.
All three main unionist parties believe that Junts pel Sí and CUP, because they failed to get 50 per cent of the popular vote, lack the legitimacy for Monday's dramatic move.
"You want to divide a country by raising a frontier within the European Union," Cuitadans Catalan leader Inés Arrimadas, pictured below, told pro-independence deputies, adding "the independence referendum was lost".
But Ms Arrimadas - whose party has swelled in popularity amid strong anti-politics mood across Spain - also tried to move to capitalise on corruption affecting Mr Mas's party, Convergència, part of the loose Junts Pel Si alliance.
She told her parliamentary opponents: "You are using the legitimate sentiment of many Catalans who want independence for your own personal benefit."
Mainstream Spanish parties, including the PP, have also faced corruption scandals in recent years.
Background: Who Really Won September's Catalan elections?
In September Yes parties won 48 or so per cent of the vote and 72 of the 135 seats in parliament.
Ciutadans, Socialists and the PP together got 39 per cent on a No ticket.
Other parties have said they did not want their votes to be counted as either Yes or No.
One of those is another anti-establishment group, Podemos. Its spokesman on Monday said the vote in parliament was an "insurgency" and joined unionists in casting doubt on its legitimacy.
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