Farage, who was brought on stage in 2016 by Trump following the Brexit vote, made a surprise appearance at the Make America Great Again at Phoenix Goodyear Airport in Arizona on Wednesday.
Telling supporters that Farage was “one of the most powerful men in Europe”, Trump was keen to maximise turnout in Arizona, where polls show opponent Joe Biden holding a slim lead.
In a speech full of praise for the US president, Farage hit out at Trump critics and “the establishment”.
He said: "Four years ago I was honoured to come to America to bring the Brexit message.
"The message that you can beat the establishment and that is what Donald Trump did.
"He beat the pollsters. He beat the media. He beat all the predictions. And here's the worst bit, they've never forgiven him for it.”
The Brexit Party leader urged voters to get behind Trump, who Farage said stood for “decency and plain speaking”.
Watch: Trump casts his ballot in US election
He added: "This is the single most resilient and brave person I have ever met in my life.
"You are voting for the only current leader in the free world who has the guts to stand up for the nation state, to fight for patriotism, to fight against globalism.”
Highlighting the president’s achievements, Farage said that Trump is "bringing Israel together with Arab nations in a way that nobody ever believed was possible”.
Trump thanked Farage as he left the stage, saying: "I'm glad I called him up. That's something.”
Farage later tweeted a clip of his speech, adding alongside: “Very surprised to be asked onto the stage, delighted to do so. He is on top form.”
Arizona, which Trump won narrowly in 2016, is seen as a key state in next week’s election, while polls continue to point to an overall Biden victory.
Watch: Are elderly voters deserting Trump?