The presidential election was deadlocked after an attempt by the centre-right to impose its own candidate ended in failure.
Italy has sought to accelerate the process of electing a new president after days of deadlock that has paralysed Prime Minister Mario Draghi's government, but parliament remained bitterly divided.
Political leaders on Friday agreed to hold two rounds of voting a day rather than just one after the four ballots failed to produce anything resembling a winner since Monday.
But the first ballot on Friday resulted in failure, after the leftist bloc in parliament abstained in protest at the candidate proposed by the right.
And the sixth attempt in the evening collapsed before it started after the right-wing bloc said it would abstain in response to the earlier boycott.
Two more votes were scheduled on Saturday, and negotiations continued between the disparate parties that share power in Draghi's national unity government.
Absolute majority needed
But with Draghi tipped for the job, this year's race risks destabilising the government and deepening fractures among parties already jostling ahead of elections in 2023.
On Friday, Matteo Salvini's League party for the first time officially put forward a candidate on behalf of the right-wing bloc, Senate president Elisabetta Casellati.
In the end, Casellati — who if elected would be Italy's first female head of state — secured just 382 votes, not even all of those commanded by the right-wing parties.
The winner must secure an absolute majority of the electoral college, which comprises 1,009 MPs, senators and regional representatives.