Giorgio Napolitano, 87, secured the required 504 votes in parliament.
Politicians had turned to the widely-respected president after five rounds of voting failed to produce a successor.
A caretaker government has been governing Italy following February’s inconclusive general elections.
The political deadlock has compounded concern about the stability of Italy whose economy, the third-biggest in the eurozone, is mired in recession.
On Saturday, Giorgio Napolitano became the first president in Italian history to secure a second seven-year term.
He easily won the simple majority of votes out of 1,007 electors.
Giorgio Napolitano put forward his candidacy after the appeal by main party leaders – both on the left and right.
“I consider it necessary to offer my availability,” said Giorgio Napolitano, who had been due to step down on May 15.
“I cannot shun my responsibility towards the nation,” he added.
Italian party leaders earlier expressed concern over a “grave situation”, urging parliament to “show unity” in re-electing widely-respected Giorgio Napolitano.
Outside the parliament building in Rome, protesters held a rally against the push for Giorgio Napolitano’s re-election.
Many demonstrators were supporters of Beppe Grillo, the leader of the 5-Star Movement.
Beppe Grillo denounced giorgio Napolitano’s re-appointment as a “coup d’etat”.
Parliament began trying to elect a new president on Thursday, but MPs voted five times without producing a clear winner. In increasing desperation they turned to Giorgio Napolitano, who was supposed to retire.
On Friday, the leader of Italy’s centre-left alliance, Pier Luigi Bersani, promised to step down as soon as a new president was elected.
Pier Luigi Bersani announced the news to his Democratic Party (PD) after many centre-left MPs refused to back his preferred candidate for president.
The centre-left failed to gain an overall majority at February’s general election despite coming first.
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