Watching proceedings in parliament on two large screens, they clapped and shouted "independence" in Catalan before singing the regional hymn, many raising their fists.
Some celebrated by drinking Cava, a sparkling wine produced in Catalonia, and hugged each other.
"It has cost us so much to get here," 38-year-old social worker Judith Rodriguez told AFP in the crowd, with tears in her eyes.
"I am very emotional about finally moving forward, to be able to build a republic, a new country, from scratch," added Rodriguez, who wore a t-shirt with the slogan "fem pais" or "let's build a country".
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Reacting after the vote, EU President Donald Tusk said that Madrid "remains our only interlocutor", but nevertheless urged the Spanish government to go easy with its planned temporary takeover of the semi-autonomous region.
"I hope the Spanish government favours force of argument, not argument of force," he tweeted.
Rodriguez's partner Jose Ligero, a 43-year-old property manager, said the international community did not understand what was happening in Catalonia.
Two influential grassroots independence groups, the Catalan National Assembly and Omnium Cultural, had urged its followers to gather outside the parliament during the vote.
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