Giorgia Meloni, leading a center-right coalition, is on track to become Italy's first woman prime minister ever and its first far-right leader since Benito Mussolini. The main center-left group has conceded defeat.
Speaking early Monday, Meloni said Italians had sent "a clear message" in backing her alliance.
"If we are called upon to govern this nation, we will do so for all Italians, with the aim of uniting the people, of exalting what unites them rather than what divides them," she told reporters. "We will not betray your trust."
Her remarks came shortly after the main center-left group, the Democratic Party, conceded defeat.
"This is a sad evening for the country," Debora Serracchiani, a senior PD lawmaker, told reporters in the party's first official comment on the result. "[The right] has the majority in parliament, but not in the country," Serracchiani said.
How are world leaders responding to the election results?
French President Emmanual Macron's office said in a statement that France respects the electoral results, and "as neighbors and friends, we must continue to work together."
"It is within Europe that we will overcome our common challenges," the Elysee Palace said in a statement.
US Secretary of State Antony Blinken said Monday the United States looked forward to working with Italy's new government on shared goals.
"We are eager to work with Italy's government on our shared goals: supporting a free and independent Ukraine, respecting human rights and building a sustainable economic future," Blinken said.
British Prime Minister Liz Truss congratulated Meloni on "her party's success in the Italian elections" in a tweet.
"From supporting Ukraine to addressing global economic challenges, the UK and Italy are close allies," Truss said.
What did exit polls indicate?
Polls closed at 11 p.m. local time (2100 GMT) on Sunday. Exit polls had shown the alliance, led by Meloni's Brothers of Italy party, securing around 45% of the vote. Meloni's own party had 26% of that by itself, as the strongest single group in the polls.
The center-left alliance, led by the Democratic Party, was the second-strongest bloc, with 29%.
The populist 5 Star Movement grabbed 16.5%, following reports of a last-minute surge in support after a polling moratorium had been imposed.
Some 51.5 million people were eligible to cast ballots. The Interior Ministry put the overall turnout at 64% — far lower than the 2018 election, which had seen a record low turnout of 73%.
The projections indicated that the center-right alliance was winning between 227 and 257 of the 400 seats in the lower house of parliament and 111-131 of the 200 Senate seats.
The center-left alliance, led by the Democratic Party, was projected to have secured 88 seats in the lower house and 42 seats in the Senate.
Who is part of the winning coalition?
Meloni's Brothers of Italy party is in an alliance with the anti-migrant League party of Matteo Salvini, as well as the center-right Forza Italia led by former Prime Minister Silvio Berlusconi.
Meloni campaigned on a motto of "God, country and family." The 45-year-old nationalist has downplayed her party's post-fascist roots and sought to promote it as a mainstream conservative group.
She has rejected accusations of being a fascist, and increasingly toned down some of the more far-right rhetoric.
However, in June, she railed against a so-called LGBT lobby, "mass immigration" and "big international finance."
Although she has been known for her euroskeptic stance, she has abandoned her calls for Rome to ditch the eurozone. Instead, she wants Italy to assert its interests more in the European Union.
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How have right-wing politicians in Europe reacted?
"No threat of any kind can stop democracy," Bardella said. "The people of Europe are raising their heads and taking their destiny back into their own hands."
EU takes pragmatic tone
The European Commission said it hoped for a positive relationship with the next Italian government.
EU spokesman Eric Mamer said it was normal for the commission to work "with the governments that emerge from elections."
"This is no different in this case. Of course, we hope that we will have constructive cooperation with the new Italian authorities," he added.
However, the International Auschwitz Committee voiced shock at the election result.
"For all survivors of the Holocaust and the heirs of the Italian resistance, one of the most important resistance movements against fascism in Europe, this election outcome is a shocking and sad event," the committee's Executive Vice President Christoph Heubner said.
Italy's complicated electoral system was revised in time for the 2018 elections, meaning that a party or group is no longer guaranteed a majority if it can attain 40% of the vote as was the case beforehand.
Nevertheless, polls from two weeks before the ballot, after which a freeze on opinion polling took effect, suggested that Meloni's right-wing alliance was poised to claim majorities in both houses.
Given the complicated electoral system and the likelihood of coalition negotiations, the first session of the new parliament and formation of a new government is liable to take weeks, as it tends to in Germany after a national vote.