A right-wing alliance led by Giorgia Meloni's Brothers of Italy party was on course for a clear majority in the next parliament, giving the country its most right-wing government since World War Two.
Meloni, as leader of the largest coalition party, was also likely to become Italy's first woman prime minister.
Meloni, 45, plays down her party's post-fascist roots and portrays it as a mainstream conservative group. She has pledged to support Western policy on Ukraine and not take undue risks with the third largest economy in the euro zone.
However, the outcome is likely to ring alarm bells in European capitals and on financial markets, given the desire to preserve unity in confronting Russia and concerns over Italy's daunting debt mountain.
An exit poll for state broadcaster RAI said the bloc of conservative parties, that also includes Matteo Salvini's League and Silvio Berlusconi's Forza Italia party, won between 41% and 45%, enough to guarantee control of both houses of parliament.
"Centre-right clearly ahead both in the lower house and the Senate! It'll be a long night but even now I want to say thanks," Salvini said on Twitter.
Italy's electoral law favours groups that manage to create pre-ballot pacts, giving them an outsized number of seats by comparison with their vote tally.
RAI said the right-wing alliance would win between 227 and 257 of the 400 seats in the lower house of parliament, and 111-131 of the 200 Senate seats.
Full results are expected by early Monday.
RECORD LOW TURNOUT
The result caps a remarkable rise for Meloni, whose party won only 4% of the vote in the last national election in 2018, but this time around was forecast to emerge as Italy's largest group on around 22-26%.
But it was not a ringing endorsement, with provisional data pointing to turnout of just 64.1% against 74% four years ago -- a record low number in a country that has historically enjoyed a high level of voter participation.
Although heavy storms in the south appeared to have deterred many from voting there, participation fell across a swathe of northern and central cities, where the weather was calmer.
Italy has a history of political instability and the next prime minister will lead the country's 68th government since 1946 and face a host of problems, notably soaring energy costs and growing economic headwinds.
Initial market reaction is likely to be muted given that opinion polls had forecast the result accurately.
"I don't expect a big impact although it's not necessarily the case that Italian assets will do particularly well tomorrow (Monday) given how the market is starting to treat Europe and countries with worrisome public finances and exposure to the crisis and Ukraine," said Giuseppe Sersale, fund manager and strategist at Anthilia in Milan.
Italy's first autumn national election in over a century was triggered by party infighting that brought down Prime Minister Mario Draghi's broad national unity government in July.
The new, slimmed-down parliament will not meet until Oct. 13, at which point the head of state will summon party leaders and decide on the shape of the new government.
(Additional reporting by Gavin Jones, Rodolfo Fabbri and Giselda Vagnoni in Rome, and Danilo Masoni in Milan; Editing by Keith Weir)
