The mayor of Charlottesville, where the now-cancelled rally was taking place, said he was "heartbroken" at the death. "I urge all people of good will-go home". The protests continued into Saturday and turned deadly when a vehicle plowed through a crowd of counter-protesters.
For now, the identity and motive of the driver are unknown.
Republican U.S. Senator Cory Gardner wrote on Twitter: "Mr. President - we must call evil by its name", adding "These were white supremacists and this was domestic terrorism".
President Donald Trump, speaking midafternoon from New Jersey, condemned "the egregious display of hatred, bigotry and violence on many sides" in Charlottesville. "It has been going on for a long long time". He also said "there is no place for this kind of violence in America".
Following the clashes, a state of emergency was declared by the authorities, and police and security forces were deployed in riot gears.
The Charlottesville protests, which originated to speak out against the removal of a statute of confederate general Robert E. Lee, became aggressive and risky before the rally was supposed to start at noon, resulting in multiple fights and injuries.
Anti-racism protesters waved flags from the Black Lives Matter movement, chanting slogans like "We say no to racist fear" and "No Nazis, no KKK, no fascist U.S.".
The deadly incident occurred about two hours after violent clashes broke out between white nationalists, who descended on the town to rally against the city's plans to remove a statue of the Confederal Gen. Robert E. Lee, and others who arrived to protest the racism.
President Trump earlier in the day on Twitter said Americans must unite against hate, although he didn't specifically condemn the white nationalist sentiment or Nazi symbols that appeared in Charlottesville.
Prominent Democrats, civil rights activists and some Republicans said it was inexcusable of the president not to denounce white supremacy.
DSA was one of several left-wing counter-protest groups in Charlottesville protesting the "Unite the Right" demonstration by white supremacists and white nationalists. "We have to respect each other, ideally we have to love each other".
Police said the driver was arrested moments later and was being investigated for criminal homicide.
The president's silence had been noticeable Friday night, as a few hundred tiki torch-bearing white supremacists - mostly young men - paraded through the University of Virginia campus while chanting racist taunts and flaunting Nazi paraphernalia.
"So when I watch Charlottesville, to me it's very, very sad", Trump said. Since then, the city has been a focus of white nationalists.
Charlottesville Mayor Michael Signer said he was disgusted that the white nationalists had come to his town and blamed President Donald Trump for inflaming racial prejudices with his campaign previous year.