The Green Party pushed the Tories into fifth place in England and Wales, more than doubling its tally of MEPs.
The party’s sole Westminster MP Caroline Lucas said the “tremendous” result was part of a “Green wave sweeping across the EU”.
The number of Green MEPs in England and Wales rose from three to seven as its share of the vote increased by 4.6% to 12.47%, putting the party in fourth place, comfortably ahead of the Tories on 8.81%
The party won its first seats the Eastern, North West, West Midlands and Yorkshire and Humber regions as well as holding onto seats in London, the South East and the South West.
Ms Lucas, the party’s former leader, said the surge in votes for the Greens and the Lib Dems showed that the voice of Remainers must be heard.
“The clear indication is those parties that made it their business to say our future is better off in the EU did better than the hard Brexiteers.
“Let’s make sure that is what people hear loud and clear.”
Sian Berry, co-leader of the Green Party, said: “Our message of ‘yes to Europe, no to climate change’ clearly resonated strongly with voters, many of whom will have been casting their vote for our party for the first time.
“We topped the poll in Bristol, Norwich and Brighton and Hove, and scored brilliant seconds in Sheffield, Cambridge and Oxford. ”
She added: “There is clear evidence from this of strong support for the UK remaining in the European Union, but also for tackling the causes of Brexit – the massive damage done to so many communities by austerity, tax-dodging and diminution of workers’ rights.”
Green parties also fared well in other parts of the EU, including in Germany, where they were on course to take second place, and in Ireland, where the party’s candidate Ciaran Cuffe topped the poll in the Dublin constituency.