BUDAPEST — A conservative provincial mayor has been chosen to face off against Hungarian Prime Minister Viktor Orban in next year's election, BBC reported on Monday.

Peter Marki-Zay, a political outsider with no party affiliation, won an opposition run-off primary on Sunday.

He will now lead a united opposition into the parliamentary elections.

Opinion polls suggest he has the best chance of ousting the right-wing prime minister, whose Fidesz party took office in 2010.

"We want a new, cleaner, honest Hungary, not just to replace Orban or his party," Marki-Zay told jubilant supporters in Budapest.

Marki-Zay, 49, a practising Catholic and father of seven, was 20 points ahead with around half the votes counted when his centre-left opponent Klara Dobrev congratulated him on his victory.

"From now on I support Peter Marki-Zay," Dobrev said during a concession speech, urging opposition unity after a bruising election campaign.

For years Fidesz has benefited from the fragmentation of opposition parties.

But for the first time since he came to power, Orban will now face a united front of opposition parties that also includes the socialists, liberals and the formerly far-right, now centre-right, Jobbik.

Marki-Zay has sold himself as a palatable option for voters from the left and right, including those tired of Mr Orban's often divisive policies, such as anti-immigration and anti-LGBTQ drives.

The new opposition leader, who has lived in both the US and Canada, made a name for himself in 2018 when he won the mayoral election in the southern town of Hodmezovasarhely, which was considered a Fidesz stronghold.

"We want to get rid of the big boys bullying the whole class," Marki-Zay said at the time.

But there is a long road ahead for Marki-Zay, who has vowed to stamp out corruption and heal divisions in society. Polls suggest there is little between Fidesz and the opposition alliance.

In a statement, Fidesz said their rival had signed a pact with the political left to help them return to power, and raise taxes, labelling him a "career leftist".