The far-right League party stormed to victory in Italy and the National Rally won in France, but nationalists were less impressive in Germany and further afield, posing questions on their future effectiveness.
The Spanish social democrats becomes the biggest national group among the European socialists, after winning the Spanish European election - which also sees a Catalan separatist in jail elected as MEP.
Romanian voters have backed the president's justice reform gamble and dealt an electoral blow to the governing Social Democratic Party (PSD) in the European elections, as the centre-right parties surged to over 50 percent of the vote.
The League, Italy's far-right party, doubled its vote in European elections compared to the national elections in 2018, while the other governing party, the Five Star Movement (M5S), lost half of its voters.
Newcomer Brexit Party received a whopping 31.7 percent of the votes in the UK - although the four pro-Remain parties received more votes together.
European voters upset the status quo in the new European Parliament, breaking the monopoly of the mainstream centre-right and centre-left. Here are the key points from the 2019 vote.
A former central banker, and political independent, Gitanas Nauseda won Lithuania's presidential election on Sunday against centre-right former finance minister, Ingrida Simonyte, in the second round of the elections. Nauseda will replace president Dalia Grybauskaite, often dubbed the Baltic nation's 'Iron Lady'. She could not run again after two terms in the post. Nauseda has pledged to maintain Grybauskaite's strict tone toward Russia.
Socialist 'Spitzenkandidat' for the EU Commission presidency, Frans Timmermans, said Sunday he wanted to forge a "progressive coalition" in the EU parliament with liberals, greens and the far-left groups. The Socialists came second with 150 seats behind centre-right EPP's 179 seats. "My worry is when [Manfred] Weber and EPP talk about stability, they mean 'let's keep things as they are', and we need to make bold decisions," he said.
Catalan former separatist leader, Carles Puigdemont, now living in exile in Belgium, won his bid for a seat in the European Parliament on Sunday night, according to Reuters. However, Puigdemont cannot take up his new role without returning to Madrid, where he faces jail. Fellow Catalonian separatist Oriol Junqueras, already imprisoned in Spain on rebellion charges, also won a seat as an MEP.
Manfred Weber, the lead candidate of the centre-right European People's Party (EPP) on Sunday said like-minded parties seeking a stronger Europe need to unite and join forces. "That is my invitation to the socialists, the liberals, and also to the Greens - and having the figures in mind, the Greens are also the winners of the day - and that is why the Greens are possible partners," he said.
Greek prime minster Alexis Tsipras has called early national elections after his ruling Syriza party lost badly to the opposition New Democrat (ND) conservatives on Sunday night in the European Parliament elections. Elections in Greece had been expected by October, but will now be in June. Exit polls had put ND on 32-36 percent, according to the poll for six broadcasters, with the governing Syriza on 25-29 percent.
The EU political centre held together in the European elections - even if the high turnout has led to a more fragmented new parliament. Greens and liberals have made gains, while the centre-right suffered.
The ruling right-wing Law and Justice (PiS) party won EU elections in Poland with 42 percent, compared to 32 percent in 2014, beating the European Coalition, a pro-EU group, on 39 percent, exit polls said. The new Spring party of openly-gay politician Robert Biedron got six percent. The "decisive blow" for the future of Poland will come in autumn national elections, PiS leader Jarolslaw Kaczynski said.
Romanian voters punished the corruption-tainted ruling PSD party in European Parliament (EP) elections Sunday, with an 11 point drop to just 23 percent, exit polls said. Voters also said the PSD should not reverse anti-corruption reforms in a non-binding referendum the same day. The centre-right opposition PNL party came top in the EP vote with 29 percent. A new liberal bloc called USR-Plus came third with 23 percent.
A party like atmosphere has seized the Greens as a packed room of people discuss around food and drinks. Elsewhere, the centre-right EPP appear sombre, as they huddle around their computers behind closed doors.
The Greens are set to become the fourth-biggest party, according to the European Parliament's first official projections, with 71 MEPs, up from 52. The centre-right EPP would remain the biggest party with 173 MEPs. The socialists could end up with 147 MEPs, liberals with 102 and the far-left with 42. The conservative ECR is to get 58 seats, populists and nationalists could get 113 seats in total.
With 427 million possible voters, across 28 EU countries, electing 751 MEPs, it's the second-biggest democratic vote in the world. The results will come thick and fast - follow them here, via the European Parliament's official results site.
A forecast by poll aggregator Britain Elects has put the Brexit Party of Nigel Farage in first place in the UK European elections, with 24 seats. The forecast sees the Liberal Democrats gaining 14 seats, to a total of 15, with Labour losing six, to have 14 MEPs, and the Conservatives losing nine, leaving them with 10 MEPs. The Greens would pick up one seat, to have four MEPs.
Far-right Marine Le Pen's National Rally won the European elections in France on Sunday, according to exit polls, with 24 percent of the vote. President Emmanuel Macron's En Marche came second with 22.5 percent of the votes. The result, if confirmed, means a comeback for Le Pen, after her defeat by Macron in 2017 in the presidential election. The Greens came in third, with 12.5 percent, beating the conservative Republicans.
Estimated turnout for the European elections among the EU-27 member states is at 51 percent - "the highest in the last 20 years" according to a European Parliament spokesman on Sunday night. Turnout figures from the United Kingdom are expected at around 11PM Brussels time. The UK estimates may see the final overall turnout range from 49 percent to 52 percent.