The Reform UK leader also backed shooting down Russian jets that enter Nato airspace and spending frozen Russian assets to help Ukraine.
With the party riding high in the polls, rivals have sought to promote perceptions that it and its leader are weak on Moscow after Mr Farage previously said he admired the Russian president.
But seeking to toughen his line on Thursday, he told Bloomberg's The Mishal Husain Show: "Clearly, Putin is not a rational man.
"The idea that I'm soft on this is just nonsense."
Stating that "obviously, Putin is a very bad dude", Mr Farage added: "I was really hoping that Trump would bring Putin to heel, that some kind of compromise could be struck, as it's just been recently struck with Gaza and Israel. Clearly, that is not going to happen."
More than a decade ago, when asked which world leader he admired the most, Mr Farage replied: "As an operator, but not as a human being, I would say Putin.
"The way he played the whole Syria thing. Brilliant. Not that I approve of him politically. How many journalists in jail now?"
The Reform leader has expressed repeated frustration at the comments, published in 2014 by GQ, being brought up since, saying the comments were misquoted.
Labour aims to win back Reform voters by attacking the leader's "Putin fawning" following a dire set of local election results for the Government in May.
Launching the party's local election campaign in April, Sir Keir Starmer said: "[Reform] claims to be the party of patriotism. I'll tell you this, there's nothing patriotic about fawning over Putin."
"Reform has a couple of weaknesses and the Putin fawning is one of them," a Labour source told The Telegraph in May. "We know there is strong public support for backing Ukraine against the Russians."
Asked on Thursday what he would do if Russian jets crossed into allied airspace, Mr Farage said: "Gotta shoot them down."
He said frozen Russian assets should be used to provide loans for Ukraine "if they're there through illegal means".
He added that in the event of a ceasefire, he could support the presence of British troops in Ukraine as part of a UN peacekeeping force if he became prime minister.
But Mr Farage repeated arguments that "the endless eastward expansion of Nato and the European Union" contributed to Putin's decision to invade Ukraine.
In response, Sophia Gaston, a foreign policy expert, said on X: "If you say you support Nato (encouraged by the resilience of British public support) and Ukraine but blame Nato expansionism (a response to Russian aggression) for 'provoking' Russia, then you don't support Ukraine and you're not credible on European security, full stop."
John Healey, the Defence Secretary, warned last month that neither Mr Farage nor his party could be trusted with Britain's national security, accusing him and his party of "looking up to" Putin.
Reform has come under pressure after Nathan Gill, the party's former leader in Wales, pleaded guilty to accepting bribes in exchange for making pro-Russian statements while he was a member of the European Parliament.
"We had a bad apple in this bloke? Yes," Mr Farage told the Bloomberg show, adding: "I believe, 100 per cent, with all my heart, there's nobody else."