The movement celebrated a shock success in 2013's general election when it snapped up a whopping 25.5 percent of the votes, becoming the second biggest political force behind the centre-left Democratic Party.
"Today we are ready, much more than in 2013," Luigi di Maio, one of Five Star's most prominent members, told AFP.
Di Maio, 29 years old and the youngest deputy president of the lower house of parliament in Italian history, has become the new face of the movement, displacing its loud and truculent founder, who is now rarely seen in public.
The pair could not be more different: where bearded, wild-eyed Grillo, 67, shouted abuse to rouse the crowds, Di Maio, who hails from Naples and studied law, speaks quietly but firmly and dresses in an impeccable suit and tie, never a hair out of place.
He has tried to restore credibility to the Five Star (M5S) after a fallout within the party forced the ex-comic to take a step back.
While Grillo called last October for the country to leave the euro "as soon as possible", Di Maio is more prudent - perhaps having watched Greece teeter on the edge of a "Grexit", which some warned could force the country to exit from the European Union.
"Our line doesn't foresee a straightforward exit from the euro", he says, insisting that it would only ever be considered if the common currency "continues to strangle our economy".
The party would like a reformed eurozone but believes centre-left Prime Minister Matteo Renzi lacks "the authority" in Europe to make that happen.
Renzi, 40, is the Five Star's main adversary in the run-up to the next general election, scheduled to be held in 2018. And Di Maio - who began following Grillo back in 2007 - is often named by political watchers as the man to challenge the PM.
Along with the "Grillini", as the movement's members are known, the party's leaders have some tricks up their sleeve to woo voters.
On the up
In the 16 municipalities run by the Five Star, including Livorno and Parma, the party has already implemented a popular scheme whereby citizens can choose how a portion of their taxes are allocated.
Those elected, from local seats to the European parliament, have also renounced half their salaries for the past two years, a move Di Maio says has saved some €10 million which have been given as microcredit to small businesses.
"Around 8,000 (such companies) will have been helped by the end of the year," he said.
Though the movement has been accused of "populism", he shrugs off the label, describing the party's programme as a "concrete project based on voters' concerns, with financially assured proposals", such as a plan to introduce a minimum wage.
The Five Star party "continues to grow because Italian politics continues to be a 'rubber wall'", he says, describing the way the hopes and ambitions of the population appear to bounce straight off the walls of power and disappear into nothing.
Polls published this week show the Five Star gaining ground on the Democratic Party, with 25 percent of those polled now favouring the anti-establishment movement compared to 34 percent for Renzi's party, which has dropped in popularity since last year.
The movement is keen to seize the moment to make its mark - especially now that even the left has been hit by corruption scandals.
"It seems to us that we are elected when the Italians see all the nastiness the (mainstream) political world is capable of," he says.
His mobile phone beeps. A breaking news alert tells him that the Senate has just voted to protect a centre-right senator suspected of graft, fraud and racketeering, by refusing to strip him of his political immunity.
The vote passed thanks to several members of the centre-left Democratic Party, who were afterwards accused of having saved the senator's skin because they had received favours from him when he was chair of the budget committee.
"You see, things never change," Di Maio says with a smile.