The party captured 23.67 percent of the vote, beating the Convergence and Union (CiU) party, the biggest formation in Catalonia's local parliament, which came in second with 21.86 percent of the vote.
The CiU President of Catalonia Artur Mas put a positive spin on the result saying it was a confirmation that a planned November 9th poll on the issue of independence for the region should go ahead.
The Spanish Parliament has declared the planned unilateral vote in Catalonia illegal on the grounds that all Spaniards have the right to vote on whether a single region can become independent.
But Mas how vowed the vote will go ahead.
"It's all moving forward, not one step back," he Mas at the end of a EU electoral campaign dominated by the sovereignty debate.
ERC leader Oriol Junqueras also chalked up the victory as another step towards possible independence for the region.
"This result in the service of the November 9th referendum, and also in the service of the institutional stability of Catalonia, because this stability is indispensable for the referendum to turn out well," he said.
The strong interest in the EU elections campaign in Catalonia was also marked by a relatively high turnout — up more than 10 percent on 2009 figures to 47.6 percent.