The Eurosceptic, anti-establishment Five Star Movement was the biggest party with almost a third of the vote.
But a coalition of the far-right League and centre-right of ex-Prime Minister Silvio Berlusconi is set to win most seats in the lower house of parliament.
Forming a government may now take weeks of negotiation and coalition-building.
One of the biggest winners was League leader Matteo Salvini who declared his party had the "right and duty" to govern at the head of a right-wing coalition.
Results showed the League conquering broad swathes of Italy's north, while Five Star saw its strongest show of support in the south.
Latest results show Five Star garnering 32.3% of the vote, while the League received 17.6% of the vote and Silvio Berlusconi's Forza Italia 14%.
The ruling centre left lost ground, with Matteo Renzi's Democratic Party (PD) securing only 18.9% of the vote. La Repubblica newspaper described its failure to win a fifth of the votes as a psychological blow.
Voter turnout was estimated at 73% on Monday morning, according to interior ministry figures.