The Spanish government has said it will appeal to the Constitutional Court which is expected to annul the decree signed by Catalan leader Artur Mas.
Fired by the independence referendum in Scotland this month, 1.8 million people protested in Barcelona on September 11 to be allowed to hold their own vote.
"We want to vote," Mas said after he inked the decree calling a referendum in a ceremony at the Generalitat Palace in Barcelona.
Catalonia is Spain's economic powerhouse, although it too suffered in the property crash and resulting crisis that gripped the rest of the country from 2008 to 2012.
Proud of their Catalan language and culture, many of the region's 7.5 million inhabitants feel short-changed by the government in Madrid, which redistributes their taxes.
Catalonia formally adopted the status of a "nation" in 2006 but Spain's Constitutional Court overruled the claim.
Prime Minister Mariano Rajoy has described a Catalan vote on independence as illegal and has vowed to defend the unity of Spain.
His cabinet will meet on Monday and the government is expected to appeal immediately to the Constitutional Court.
Such an appeal would trigger a suspension of the referendum pending a final judgement from the judges.
Mas has vowed to let Catalans vote on breaking away but has also promised to respect Spanish law.
He has hinted that if the government blocks the vote, he could call early regional elections in Catalonia which would effectively act as a plebiscite on the issue.
Catalonia's regional parliament on September 19 approved a law which its leaders say authorises them to hold a non-binding "consultation" on independence.
While voters in Scotland voted by 55 percent to 45 percent to remain part of the United Kingdom, British Prime Minister David Cameron offered Scots increased autonomy if they rejected independence.
The process in Scotland was watched closely by Catalonia's leaders.
Hinting at his own ambitions, Mas said before the Scottish referendum that an independent Scotland would be swiftly re-admitted to the European Union.
But Rajoy described the independence ambitions of the Scottish National Party and Catalonia as a "torpedo" to European integration.
The Catalonian economy is bigger than the entire Portuguese economy and generates 20 percent of Spain's wealth.
Catalonia is also a popular tourist destination and home to the Barcelona football team of Lionel Messi, which is one of the world's richest sports clubs.