The former Ukip leader described a Le Pen win as “best for our country”, arguing that it would help destroy the “failed project” that is the EU.
Writing in The Telegraph, Mr Farage said: “From a UK perspective, as we enter tough negotiations, what is best for our country?
“I have no doubt that a Le Pen victory would give the EU an even bigger headache than the UK voting for Brexit, which is why the European Commission is openly backing Macron.
“She wants a positive relationship with Britain and was enthusiastic about a bilateral trade deal in the future. She is being grown-up on the issue of trade post-Brexit.”
He added: “Her victory would take much of the pressure off our negotiations. She will put France first and take her country out of the euro, which has damaged their competitiveness.
“A Le Pen victory would be the beginning of the end for this failed project.”
Mr Farage’s endorsement may not be too much of a surprise, coming off the back of his unpopular decision to back Donald Trump to be US President.
He also interviewed Ms Le Pen on his LBC radio show in March but has resisted fully endorsing her until now.
Lib Dem foreign affairs spokesperson Tom Brake criticised Mr Farage’s backing, saying the MEP’s “mask is slipping, revealing a more sinister face” than before.
Ms Le Pen, who has quit the National Front in an attempt to detoxify her brand, has campaigned on cracking down against religious minorities and immigration.
She is expected to lose the election to Mr Macron but Mr Farage predicted that she would win the next French presidential election in 2022.
Top pic: Rex