ROME • Former Italian prime minister Matteo Renzi is poised to win the leadership of Italy's ruling Democratic Party (PD) in a primary election, propelling him back to the forefront of the national political scene.

Mr Renzi, 42, resigned as prime minister in December after Italians overwhelmingly rejected a constitutional referendum.

A centrepiece of his political platform, the reform had aimed to streamline Italy's parliamentary system.

In the aftermath of the December vote and facing a rebellion from the left wing of his centre-left party, Mr Renzi in February stepped down as party leader with the aim of regaining legitimacy in a future vote.

In the primary yesterday, Mr Renzi faced two candidates considered further to the left: Justice Minister Andrea Orlando and Mr Michele Emiliano, who heads the southern Puglia region.

During the only televised debate between Mr Renzi and his two competitors, the former prime minister said he would do "everything to bring back energy, momentum and vigour to the country", and railed against "stagnation that seems to be blocking the political and institutional life" since the referendum.

An internal vote conducted by the party earlier this month suggests Mr Renzi could win hands down. He had more than a majority at 66.7 per cent, with 25.3 per cent for Mr Orlando and 8 per cent for Mr Emiliano.

Political sociology professor Lorenzo De Sio at the Luiss University in Rome said Mr Renzi's legitimacy will hinge on voter turnout.

"Rather than a competition, we are facing the legitimisation, a sort of crowning of Renzi as leader of the PD. We can expect a huge Renzi victory but with weak voter turnout. People on the left do not seem to be mobilised," he said.

"If participation rates are around a million people or less, the legitimisation of Renzi won't be strong, if it is between 1.5 million and two million, he will wind up in a stronger position," he said.

Voting ends at 2am Singapore time today.

The winner of the vote will lead the party during legislative elections slated for spring next year, unless parliamentarians come to an agreement on electoral reform before then and call for early elections.

AGENCE FRANCE-PRESSE