Renzi, the 39-year-old mayor of Florence, met for more than an hour with President Giorgio Napolitano. Afterward he said he would go to work immediately on forging a new coalition, with talks with potential partners formally beginning on Tuesday.
Renzi said he would need a "few days" before seeing whether he can succeed.
But he told reporters by the end of the month he would propose new legislation to reform Italy's electoral law to make the country more governable. By March, he promised new measures to create jobs in a country where 40 per cent of young people are without work. April and May would bring other reforms, he vowed.
"I will put all the courage, energy, and enthusiasm I can muster to deal with the most important emergency: that of the labour market," he said after the meeting.
Renzi had orchestrated a mutiny within the Democratic Party to oust Enrico Letta as premier last week, accusing him of failing to jumpstart Italy's economy, even though Italy reported its first positive GDP in nearly three years that same week.
Renzi's first challenge is to form a coalition government that can win confidence votes in both houses of Parliament. That's no easy task, given that his aggressive power-grab has alienated even some within his own Democratic Party.
Outside the Quirinale palace on Monday, the small centre-right Italy Brothers party staged a protest shouting "Elections! Elections!" The party's leaders were incensed that Renzi was likely to become Italy's next premier without having ever run in a national election.
He would be the third straight premier to get the job that way.
More importantly, the New Center Right party of Angelino Alfano, who had served as Letta's deputy premier, is holding off on giving Renzi his support until he sees the premier designate's plan of action.
Silvio Berlusconi's much larger Forza Italia party has said it would remain in opposition, while the anti-establishment 5 Star Movement has boycotted the transition process altogether.
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