The 39-year-old mayor of Florence said his first priority would be to tackle relentless unemployment levels and pitiful economic growth, promising Italians he would do everything possible to alleviate "despair".
The head of the leftist Democratic Party has raised hopes in a country thirsting for change after ousting ex-premier Enrico Letta -- a member of his own party whom he accused of failing to live up to reform pledges.
"We will take the time we need, with the knowledge that there is a sense of urgency out there and this is an extremely delicate and important time," he said after being given the mandate by President Giorgio Napolitano.
"The most pressing emergency, which concerns my generation and others, is the emergency of labour, of unemployment and of despair," he added.
More From This Section
In the first test of his political prowess, the fresh-faced former Boy Scout will face a tough challenge in securing support, before facing a decisive confidence vote in parliament later this week.
Renzi vowed that if he succeeds, he will implement much-needed political and electoral reforms by the end of this month and overhaul the job market, education and the tax system in his first few months in power.
His nomination has left some analysts wondering whether he has the political maturity to succeed. "Speed is part of Renzi's personality" but "the creation of such a team is no easy task", political watcher Federico Geremicca said in La Stampa.