Catalan leader Carles Puigdemont says the Spanish region has won the right to statehood following a contentious referendum that was marred by violence.
He said the door had been opened to a unilateral declaration of independence.
Catalan officials later said 90% of those who voted backed independence in Sunday's vote. The turnout was 42.3%.
Spain's constitutional court had banned the vote and hundreds of people were injured as police used force to try to block voting.
Officers seized ballot papers and boxes at polling stations. Spanish Prime Minister Mariano Rajoy said Catalans had been fooled into taking part in an illegal vote.
'Day of hope'
More than 2.2 million people were reported to have voted, according to Catalan authorities, out of 5.3 million registered voters. A Catalan spokesman said more than 750,000 votes could not be counted because polling stations were closed and urns were confiscated.
"With this day of hope and suffering, the citizens of Catalonia have won the right to an independent state in the form of a republic," Mr Puigdemont said in a televised address flanked by other senior Catalan leaders.
"My government in the next few days will send the results of today's vote to the Catalan parliament, where the sovereignty of our people lies, so that it can act in accordance with the law of the referendum."
He said the European Union could no longer "continue to look the other way".
The Spanish prime minister spoke of a "mockery" of democracy.
"At this hour I can tell you in the strongest terms what you already know and what we have seen throughout this day. There has not been a referendum on self-determination in Catalonia," Mr Rajoy said.
Large crowds of independence supporters gathered in the centre of the regional capital Barcelona on Sunday evening, waving flags and singing the Catalan anthem. Anti-independence protesters have also held rallies in Barcelona and other Spanish cities.
In another development, more than 40 trade unions and Catalan associations called a region-wide strike on Tuesday due to "the grave violation of rights and freedoms".
The Catalan government said more than 800 people had been injured in clashes across the region. Those figures included people who had suffered relatively minor complaints such as anxiety attacks.