With dozens of new lawmakers from an Italian protest movement still dazed after a shock election success, the party's former comedian turned activist leader was suddenly in the driving seat on Tuesday.

Beppe Grillo's Five Star Movement captured more than a quarter of the vote for the lower house, incredibly becoming the biggest individual party in Parliament.

"Grillo will play a decisive role. He has to decide whether to strike a limited agreement with the left or to go for fresh elections," said Roberto D'Alimonte, a politics professor at Rome's LUISS University.

"All the cards are in his hands," D'Alimonte said.

Grillo set up his group in 2009, initially as one of several citizen movements against then prime minister Silvio Berlusconi.

Many of the new lawmakers are very young - some are close to the minimum age of 25 for entering the lower house - virtually all the candidates were newcomers to politics including students, housewives, doctors and laid-off factory workers.