SEOUL, May 1, 2025 (BSS/AFP) - South Korea's Supreme Court on Thursday overturned a ruling that found a presidential frontrunner not guilty of violating election law, potentially scuppering Lee Jae-myung's chances of running in the vote.

The June 3 election will decide who replaces impeached ex-president Yoon Suk Yeol, who was removed from office over his ill-fated declaration of martial law.

Former opposition leader Lee was cleared by a lower court in March of making false statements during a previous campaign, removing a major legal hurdle to his latest bid.

But the Supreme Court has now ordered a retrial that could see Lee, who is leading in the polls, barred from the election.

The top court ruled there had been a "legal misunderstanding" resulting in his acquittal.

Lee's statements during his unsuccessful run for president in 2022 were "deemed false claims concerning matters of sufficient significance to mislead voters in assessing the candidate's suitability for public office", the court ruled.

"A candidate seeking public office cannot be granted the same scope and degree of freedom of expression as that afforded to ordinary citizens when they express opinions or beliefs on matters of public interest," it said.

If found guilty by a lower court, Lee would be prevented from running for office for five years and could face a prison sentence or a fine of more than one million won ($700).

- Enough time to win? -
The latest Gallup poll shows the 60-year-old Lee in a considerable lead with 38 percent of support while all his rivals are locked in single digits.

The election was called in the wake of Yoon's impeachment over the martial law attempt.

While Thursday's verdict was a blow to Lee, political commentator and attorney Yoo Jung-hoon told AFP: "It usually takes about three months for a lower court to deliberate on a case remanded by the Supreme Court.

"It will be extremely difficult for the court to issue a ruling before the election."

Even if the court does rule against Lee, he could still appeal, which would "buy him enough time to win", Yoo said.

Aside from the election law violation case, Lee also faces a string of other trials on corruption allegations.

Should he win the presidency in June, these proceedings could be suspended under presidential immunity, and would resume once his term concludes.

Acting president Han Duk-soo meanwhile resigned on Thursday, hinting at a possible presidential bid.

"Two paths lay before me: one is to carry on in my current role, the other is to step down and take on a greater responsibility," Han said in a farewell address.

The 75-year-old is expected to formally announce his candidacy on Friday.