With a markedly higher turnout compared to recent years, analysts said the groundswell reflected Europeans' shifting views of the relevance of the EU. Here's what to know about the election results.
People are interested in Europe again.
One of the biggest surprises may be the resurgence in voter interest in the European Parliament, long seen as second order and framed across the continent as less important than national politics.
Turnout across the bloc surpassed 50 per cent, the highest since 1994 and the first time since voting began in 1979 that turnout has not dropped from the previous election. It was a major jump from the 2014 election, in which just 42.6 per cent of eligible voters took part.
The results reflected "a certain wake-up call,'' said Martin Selmayr, secretary-general of the European Commission, the executive arm of the bloc. "With Donald Trump and Vladimir Putin,'' he said, people realise that "if you don't engage in this European project you can lose a lot.''
Marginal success for populist candidates.
The election was seen by some as a gauge on the rising influence of populism in Europe, which has made marks in national elections from Italy and France to Hungary and Poland in recent years.
Populist parties made a notable impact, clinching about 25 per cent of Parliament seats, compared to the roughly 20 per cent they secured in the last election. But it was hardly the populist wave that candidates like Matteo Salvini of Italy and Marine Le Pen of France had hoped for after their attempts to present a united front before the vote.
"The so-called populist wave, I think it was contained," Selmayr said, adding: "All the democratic pro-European forces will need to work together.''
In Italy, Salvini's far-right, anti-immigrant League party did very well, getting some 34 per cent of the vote, according to provisional results, supporting his aspiration to become a major voice within the bloc.
In France, the far-right party of Le Pen — once known as the National Front and rebranded as the National Rally — delivered an embarrassing blow to the party of President Emmanuel Macron, long framed as the Continent's new leader for pro-Europe policies, by narrowly beating his party, La République En Marche, or the Republic on the Move.
Le Pen's party won fewer seats than five years ago, but the symbolism was clear.
The populist gains on a national level may not translate into influence on the European level, however. The movement looks very different from country to country, with priorities varying in each nation and disagreements among them on major issues like Russia and the European budget.
These disjointed policies and the strong egos involved will make it harder for those parties to forge effective alliances.
Populist parties tended to do better in southern Europe than in northern Europe, based on early numbers. In the Netherlands, the PVV party of the Dutch nationalist politician Geert Wilders lost every seat in Parliament and Social Democrats gained the majority of that country's votes.
The established centre held but has to adapt.
For the past 40 years, the European Parliament has been run by centrist parties, dominated by the centre-right European People's Party group, and the Progressive Alliance of Socialists and Democrats on the centre left.
Combined, they long held the majority of parliamentary seats, but that is no longer the case: Rising support for smaller populist parties, the Greens and liberals has weakened the influence of centrists.
Now, these groups will have to work more closely with liberal members of Parliament to create a working majority. This could shift priorities within the legislature and change the type of issues that rise to the fore.
Manfred Weber, the leading candidate for commission president from the European People's Party, acknowledged that "those who want to have a strong European Union have to join forces." But he added that his group would not cooperate "with any party that doesn't believe in the future of the European Union."
Britain voted on one issue: Brexit.
There was one issue on the table in Britain, the country's looming withdrawal from Europe. The vote underlined the divisions between those who want Brexit and those who want to abandon it.
Estimates indicated that the Brexit Party led by Nigel Farage was on course to take 31 per cent of the vote. A single-issue party that did not exist four months ago was able to pull votes away from the country's establishment parties, which were perceived as having badly mismanaged Brexit, three years after a referendum on EU membership.
The party will be one of the largest in the European Parliament, with more seats even than Salvini's party. At least so long as Britain remains a member, that is.
Farage campaigned on Britain leaving by the end of October, with or without a withdrawal deal. But that will be up to Britain's national government, where the Brexit Party has no seats.
Liberal Democrats, who campaigned on the slogan "Bollocks to Brexit" and planted themselves firmly on the other end of the spectrum, followed with an estimated 18 per cent of the vote.
The Conservative and Labour parties had their worst European election results in decades, estimated to get just 8 per cent and 14 per cent of the vote, respectively. Labour in particular suffered because of an ambivalent stance toward Brexit that has confused voters.
Farage told the BBC he felt the vote was a reflection of "the real sense of frustration out there."
"The parties that break promises do badly in elections," he said, pointing to the losses for both the Conservatives and Labour.
The Green Party had broad — and surprising — success.
The Green Party made gains across Europe, from Germany to Portugal and across the Nordic countries, based on early figures, with some analysts framing the rising support as a "green wave" of voters. Climate change, a surge of young voters and anger at existing policies seem to be behind it all, leaders of the movement say.
Bas Eickhout, a Dutch member of the European Parliament and a Green candidate for the European Commission presidency, thanked voters as results poured in. The Greens, he said, were "very clearly asking for change, asking for change for a new Europe, a Europe that is fighting climate change, a Europe that is looking for a green transition in a socially just way."
In Germany, the rise of the Green Party, which secured more than 20 per cent of that country's vote, is being seen as the big story of the election. The centre-left Social Democrats suffered their worst defeat in decades, with many voters on the left, particularly young people, turning instead to the Greens.
The Green Party also saw a surge in Ireland, where it previously held no seats, at the expense of Prime Minister Leo Varadkar's Fine Gael, particularly in its supposed stronghold in the capital, Dublin. In Britain, where Brexit dominated the agenda, the Greens gained a record seven seats.
Written by: Steven Erlanger and Megan Specia
© 2019 THE NEW YORK TIMES