Trump repeated his claim that Democratic rival Hillary Clinton "is a bigot who sees people of colour only as votes".
Clinton scoffed at that accusation during an interview on CNN. "He is taking a hate movement mainstream," she said, arguing Trump is "very much peddling bigotry and prejudice and paranoia".
Taking the stage to wild applause, Farage said he came "with a message of hope and optimism".
"We did it - we made June 23 our independence day when we smashed the establishment.
"We reached those people who have never voted in their lives but believed they could take back control of their country, take back control of their borders, and get back their pride and self-respect."
Farage criticised US President Barack Obama, who had urged the British to stay in the EU, saying he "talked down to us, as if we were nothing".
While he didn't explicitly endorse Trump for president, he made it clear who he would not vote for given the chance.
"I could not possibly tell you how to vote in this election," he told the crowd. "But, you know, I get it. If I was an American citizen, I wouldn't vote for Hillary Clinton if you paid me. In fact, I wouldn't vote for Hillary Clinton if she paid me."
Saying "the parallels are there" between what was happening in the US and what happened in Britain, Farage said American voters had a "fantastic opportunity" to "beat the pollsters ... the commentators ... Washington".
"And you'll do it by doing what we did for Brexit in Britain. We had our own people's army or ordinary citizens ... If you want change, you better get your walking boots on, you better get out their campaigning, and, remember, anything is possible if enough decent people are prepared to stand up against the establishment. "
Farage is thought to be the first British politician to address a Republican presidential election rally.