Fields ― a 21-year-old extremist associated with the hate group Vanguard America ― faced charges of first-degree murder and other felonies over the attack, in which he intentionally sped into protesters after the "Unite the Right" rally on August 12, killing one and injuring dozens more.
Unite the Right, called to oppose Charlottesville's decision to remove a Confederate statue, was the largest white nationalist rally in the United States in recent decades. Fields' mother, Samantha Bloom, who is disabled, left the courthouse in a wheelchair without commenting. The jury is set to return on Monday to determine his sentence.
Fields sat expressionless between his two attorneys as the verdict was pronounced, glancing briefly at spectators in the crowded courtroom.
Heyer, a 32-year-old paralegal, was demonstrating with dozens of others against the "Unite the Right" rally when Fields drove his auto into the crowd after a day of tense clashes between members of alt-right groups and those opposed to their presence.
In it, Fields said that he was defending himself from "a violent mob of terrorists".
The judge ruled that the text would be allowed to be entered as evidence, despite Fields' lawyer's protests, saying that it shows intent or motive of malice, according to The Associated Press.
"I saw Heather Heyer up in the air and remember thinking to myself, 'That's what someone's eyes look like when they are dead'". Her death came after police forced the rally to disband after participants had clashed with counterdemonstrators earlier.
Prosecutors, though, said Fields was enraged when he drove more than 500 miles from his apartment in OH to take part in the rally - and later chose to act on that anger by ramming his two-door muscle vehicle into the crowd.
The night before, the Unite the Right protesters had staged a torch-lit march through the nearby University of Virginia campus, chanting racist and anti-Semitic slogans.
President Donald Trump was widely condemned after he said "both sides" were to blame for the violence.
Fields was participating the Unite the Right rally on the day of the attack. He entered a not guilty plea in both the Circuit Court case and to the federal charges. Heyer's mother, Susan Bro, listened intently as the jury was polled about the verdict.
In addition to first-degree murder, which carries a possible life sentence, James Alex Fields Jr, 21, was found guilty of five counts of aggravated malicious wounding, three of malicious wounding, and one hit-and-run count.
Hundreds of Ku Klux Klan members, neo-Nazis and other white nationalists had streamed into the college town of Charlottesville for one of the largest gatherings of white supremacists in a decade.