Maciej Maciak, a journalist and leader of a group called the Prosperity and Peace Movement, answered in the affirmative when asked by another candidate during the debate on Monday if he admired Putin.
"Yes, none of us here in Poland would be able to withstand such pressure," Maciak said, referring to international condemnation of Moscow's war against Ukraine.
"This proves that he is a very good politician," Maciak added, defending the Russian leader.
His remarks, followed by applause from a member of the audience, drew a sharp rebuke from front-runner Rafał Trzaskowski, Polish state news agency PAP reported.
"What we've just heard is something unbelievable," said Trzaskowski, the mayor of Warsaw and deputy leader of the ruling Civic Platform (PO) party.
"Applauding Putin at a time when he is murdering people, killing children, allowing rapes in Ukraine ... I have really never seen anything like that in my life. I think that at least on this one issue, all of us standing here agree," Trzaskowski added.
Fellow candidate Marek Jakubiak noted that Maciak had been accused of harbouring pro-Russian views during Moscow’s war on Ukraine "and even of being a Russian agent."
Another long-shot candidate, Krzysztof Stanowski, accused Maciak of maintaining contacts with "a person linked to Russian propaganda."
"I see that you have praised how the Russians are rebuilding Mariupol and constructing new, beautiful buildings there. I have to admit, this is quite bizarre," Stanowski said.
The southern Ukrainian city of Mariupol was nearly razed by Russian forces at the start of Putin's invasion of Ukraine in 2022.
In March 2023, the Hague-based International Criminal Court issued an arrest warrant for Putin, accusing him of being responsible for war crimes committed in Ukraine.
All 13 Polish presidential candidates took part in Monday's debate, fielding questions from one another and clashing over issues including the economy, defence, migration, foreign policy and national security.
The debate also exposed deep divisions over healthcare, housing, abortion and minority rights as the country counts down to the presidential election next month.
Poles will vote on May 18 to elect their next president. A second round will be held on June 1 if no candidate wins an outright majority.
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Source: TVP Info, TVN24, PAP