ROME -- Italian lawmakers elected Sergio Mattarella, a constitutional Court justice widely considered to be above the political fray, as the nation's new president on the third day of voting Saturday.

Mattarella's election as head of state was clinched when he amassed 505 votes -- a simple majority. The 73-year-old former minister with centre-left political roots went on to garner a total of 665 votes from the 1,009 eligible electors.

Known as a man of few words, Mattarella cemented that reputation with his first remarks to the nation.

"My thoughts go, above all, to the difficulties and hopes of our fellow citizens. That's enough," he said, referring to the grim economic situation, in comments made at his court office just down the street from the presidential palace.

Italy is mired in recession and unemployment has hovered about 13 per cent nationally. Young Italians are increasingly seeking work abroad.

Renzi pushed hard for Mattarella's election, and some of Renzi's rebellious Democrats resented the premier's imposing his choice on them. Mattarella's victory signals that Renzi for now succeeded in closing fractious ranks, including former Communists, in the governing coalition's main party.

"Thanks for being serious," Renzi and some loyalists wrote in a text message to Democrats during the balloting, the Italian news agency ANSA reported.

Former Premier Silvio Berlusconi's centre-right opposition vowed to cast blank ballots. While acknowledging Mattarella's credentials to be guarantor of the Constitution and arbiter in political crises, they insisted Renzi should have reached agreement first with Berlusconi on a candidate.

Mattarella raised conflict-of-interest concerns when media mogul Berlusconi jumped into politics two decades ago. He also resigned as education minister in 1990 to protest legislation that helped Berlusconi transform what started out as several local channels into a business empire including Italy's three main private TV networks.

Mattarella, a Sicilian, was first elected to Parliament in 1983. His Christian Democrat party collapsed in corruption probes of the 1990s, but Mattarella was unscathed. His older brother, Piersanti Mattarella, governor of Sicily, was killed in 1980 by the Mafia.

The silver-haired Mattarella, a widower with three grown children, has been living in the modest quarters of constitutional Court justices in Rome. He will take the oath of office, for a seven-year term, on Tuesday.

A year ago, Berlusconi pledged his support for the electoral reform agenda of Renzi, who had just assumed the Democratic Party leadership. Buoyed by the deal, Renzi quickly pushed fellow Democrat Enrico Letta out of the premiership. Berlusconi lost his Senate seat because of a tax fraud conviction but is keen on keeping political influence.

Reforms include changing Italy's electoral law to make governments more stable. Whether Berlusconi, irked over Renzi's picking the presidential candidate, will renege on the reforms deal is unclear. A pro-Berlusconi lawmaker, Maurizio Gasparri, predicted the media mogul's centre-right lawmakers might be "less generous" with support.

Former Berlusconi allies now in Renzi's coalition chafed at the unilateral choice of the Mattarella candidacy. But the government's short-term survival seemed little threatened. Politicians are generally uneager to provoke a crisis that could bring early elections, with voters exasperated over their leaders' failure so revive the economy.

Renzi's choice of Mattarella as a nominee despite Berlusconi's opposition "will undoubtedly increase friction within and without the ruling coalition," London-based Eurasia Group analyst Federico Santi said in a statement on the eve of the successful balloting. "It may complicate reform progress at the margin. However, it will not derail reforms or threaten political stability."