The staunch Brexiteer said he could not understand why the Prime Minister welcomed French centre-left political Emmanuel Macron but would not afford the same hospitality to Ms Le Pen.
Mr Macron was invited to London by Mrs May but stood outside the front door of No10 to urge his citizen to leave Britain.
Speaking on his LBC show, Mr Farage warned that Ms Le Pen could be the next French leader and the country should learn its lesson over its dismissal of Donald Trump during the US presidential campaign.
Nigel Farage has told the Theresa May to show "respect" to Marine Le Pen
Mrs May, if you’re listening, it is not impossible that Marine Le Pen could win these elections
The 52-year-old said: “Quite why the British Prime Minister promoting a socialist candidate to be president of France who absolutely believes in the European project, I don’t know.
“Why if she’s doing that does she refuse to meet Marine Le Pen who at the moment appears to be the favourite to win the first round.
“Surely it is crazy for the British government to get involved in foreign elections to this degree and not show respect to both sides in this argument.
“Indeed isn’t it rather reminiscent of what almost everybody in Britain did by backing Hillary Clinton and saying Trump was a baddy and yet he won.
Things you didn't know about Marine Le Pen Mon, February 20, 2017
Marine Le Pen is a French politician who is the president of the National Front, a national-conservative political party in France and one of its main political forces.
Play slideshow AFP/Getty Images 1 of 10
Described as more democratic and republican than her nationalist father, she has led a movement of "de-demonization of the Front National" to detoxify it and soften its image
“Mrs May, if you’re listening, it is not impossible that Marine Le Pen could win these elections.”
Meanwhile, Pierre Moscovici, France’s former finance minister, said the Front National leader winning the French presidency "must not happen".
His comments come after a host of polls predict the anti-establishment candidate will crush her rivals in the first round of the French presidential election on April 23.
Mr Moscovici said: "If Marine Le Pen comes in office, if she asks for a referendum on Frexit, what would Europe be about? Europe was founded precisely in order that France and Germany and others work together in a common project.
“That is why precisely it cannot happen, it won't happen, it must not happen.”
On his trip to Westminster Central Hall, Mr Macron, 39, openly said he wanted “banks, talents, researchers, academics and so on” to cross the Channel and join him in what he hopes will be his Paris headquarters after the second round of the French election on May 7.