No party or coalition received enough votes to rule alone, and Italy now faces a hung parliament, in what European Commission chief Jean-Claude Juncker described last month as the "worst-case scenario" for Europe.
A right-wing coalition of parties won the most seats of any bloc in parliament with about 37% of the vote. The big winner in that group was the anti-immigrant and xenophobic League -- formerly the Northern League -- which garnered more votes than the center-right Forza Italia, its potential coalition partner.
The result will be met with alarm by European leaders who feared that big wins for Italy's anti-establishment parties would spell further trouble for a continent already struggling to cope with the destabilizing rise of populist and far-right movements in France, Germany and elsewhere.
- The right-wing coalition cobbled together by Silvio Berlusconi won the most combined votes at 37%, but the League came out on top of the bloc, winning roughly 17.4% of the votes to Forza Italia's 14%. The swing toward the League, led by Matteo Salvini, looks set to give the party as many as 123 seats in the lower house, up from 22 seats, an almost six-fold increase.
- Berlusconi's Forza Italia party fared worse than expected, and the former prime minister appears to have failed in his attempt to position himself as the election's kingmaker.
- With around 32.7% of the vote, M5S outperformed final opinion polls. The party dominated in the south of Italy, receiving almost one in two votes in a region where youth unemployment is historically high.
- Italy's center-left coalition had a bad night, mustering about 23% of the vote. It is likely to end up as the third-largest group in parliament behind the right-wing coalition and M5S.
- Italy looks set to enter a period of political deadlock -- facing weeks, if not months, of negotiations between groups with competing interests to form a government.
- Former Prime Minister and Democratic Party leader Matteo Renzi stepped down from his role after it suffered a worse than expected performance.
Berlusconi eclipsed by ally
As the results continued to be counted earlier in the day, the League's Salvini claimed victory during a press conference in Rome on Monday morning that will have set alarm bills ringing at European Union headquarters in Brussels.
"I have always said, I say now and I will always say that the euro is the wrong currency, and that it was a big mistake getting in it," Salvini announced. "We have it very clear that the common currency is bound to end. And we want to come prepared to that moment."
"We look towards the other European forces, that they call populist. I am and I will stay proudly populist, because the populists listen to the people, unlike the 'radical chic' that despise the workers and don't do their groceries, " Salvini said.
Though the right-wing bloc did not win enough votes to form a majority government, Salvini claimed "an extraordinary victory."
"This is the coalition that won, this is the coalition that will govern. The arrogance of [former Prime Minister Matteo] Renzi and his allies has been punished."
Fabio Bordignon, a political scientist at the University of Urbino Carlo Bo, interpreted the populist parties' strong performance as "a reflection of a strong political and economic malaise that affects Italy."
Italians have becoming increasingly frustrated after years of unprecedented migration and continued economic woes.
Seizing on this dissatisfaction, right-wing parties had touted an anti-immigration agenda, with the League pledging to put "Italians first" and advocating for mass expulsions.
Bordignon added: "[The early results] are also a demonstration that that malaise cannot be cured by building defensive barriers against populism ... The choice for the Five Star is no longer only a protest vote."
Stellar rise of M5S
But political scientist Paolo Chiocchetti said M5S would be central to the coming negotiations after it exceeded expectations.
"The big and only winners of the night are the Five Star Movement and the Lega (the League)," Chiocchetti, fellow of the Robert Schuman Institute of European Affairs at the University of Luxembourg, told CNN.
"Their rise was widely expected given the general anti-incumbency trend in Europe and the particularly harsh effect of the great recession and of austerity in Italy, whose current recovery is extremely feeble. However, they both exceeded the expectations."
The Five Star Movement had campaigned for a universal basic income, a measure especially popular in the south, where the unemployment rate, at almost 20%, is more than three times as high as in the north, according to the Italian National Bureau of Statistics (ISTAT). It appears this was a winning strategy as early projections indicated M5S had dominated the region.
Minutes after Salvini spoke, rival party leader Luigi Di Maio claimed M5S were the "absolute winners of the election," before adding that the party was "open to talks with other parties" to form a government.
"Other coalitions have no numbers to govern... So we take this responsibility," Di Maio said.
Bad day for ruling party
The disappointing performance of the governing center-left Democratic Party (PD) was captured in Italian newspaper headlines. One read "Italy belongs to Five Stars. PD sinks"; another read "Di Maio wins, Italy is ungovernable."
Although the PD is projected to have won second-most votes at about 18.7%, its center-left coalition, formed with the liberal More Europe party, could muster just short of a combined 23% and will likely end up as the third-largest group in parliament behind the right-wing coalition and M5S.
PD Leader Matteo Renzi stepped down from his role after it suffered a worse than expected performance. Speaking at a press conference on Monday, Renzi said that the party's place in government is now in opposition.
PD member and outgoing parliamentarian Andrea Marcucci said that the voters had spoken "clearly and incontrovertibly" and that "the populists had won and the (Democratic Party) had lost."
"The Democratic Party is leaving much better results to Italy than its predecessors. We will start again in the opposition," he said in the post.
Bad news for EU unity
The poll is being closely scrutinized by European leaders who are concerned by the increasingly euroskeptic sentiment on the continent and fearful of any instability in Italy, the eurozone's third-largest economy and one of the founding members of the European Union.
The rise of anti-European voices, both on the right and from the anti-establishment M5S, comes as Italians appear increasingly divided over issues such as undocumented immigration, which contributed to a rancorous campaign.
Italy is one of the main entry points into Europe for migrants from Africa, the Middle East and Asia.
Steve Bannon: 'Election is crucial'
The populist parties' gains in the polls were not lost on US President Donald Trump's former strategic adviser Steve Bannon, who was in Rome to observe the elections.
Bannon told Italy's Corriere della Sera newspaper that an alliance between the anti-immigrant League party and the populist Five Star Movement was "the ultimate dream."
"This election is crucial for the global populist movement," he said, adding that it was an issue of "sovereignty" for Italians opposed to immigration.
French far-right leader Marine Le Pen tweeted that the projected results signaled an anti-EU sentiment in the southern European country.
"The European Union is going to have a horrible evening," she said in the post.
The UK Independence Party posted its reaction to the vote on Monday, tweeting
: "The election in Italy just adds more weight that the EU project is not working. But we all know what the EU's response will be, don't we? 'More Europe.'"