An American neo-Nazi who killed an activist when he rammed his car into a group of counter-protesters during a white supremacist rally was ordered jailed for life without possibility of parole on Friday.

James Alex Fields Jr, 22, had pleaded guilty to 29 federal hate crimes charges in March in a deal with prosecutors that eliminated the possibility of a death sentence.

The charges were linked to the 29 people wounded when he drove his car through a crowd in Charlottesville, Virginia on August 12, 2017, when he killed 32-year-old paralegal Heather Heyer.

"As a result of this act of domestic terrorism that was charged as 29 hate crimes, a United States district judge this afternoon determined that Mr Fields deserved to spend the rest of his life in federal prison and imposed that sentence," said US Attorney Thomas Cullen.

According to the local CBS6 news channel, Judge Michael Urbanski said Fields was "a profoundly disturbed young man" with a history of violence and releasing him back into society would be "too great a risk to take."

Addressing the court, Fields took the opportunity to apologize for his actions, the channel added.

He will be sentenced for his first-degree murder conviction in a state court in July.

Heyer was among the activists who had gathered in Charlottesville to protest a group of white supremacists who came to the university town to protest against the removal of a Confederate statue.

President Donald Trump drew broad criticism in the aftermath of the mayhem when he spoke of "blame on both sides," appearing to establish a moral equivalence between the white supremacists and those who opposed them.

The incident turned Charlottesville into a symbol of the growing audacity of the far right under Trump.

Fields had driven overnight from his hometown of Maumee, Ohio, to support the "Unite the Right" rally to protest the removal of a statue of Robert E Lee, the top general of the pro-slavery Confederacy during the 1861-1865 American Civil War.

Dressed in a white polo shirt and khaki pants, the uniform of the white supremacists, he took part in racist, anti-Semitic and homophobic chants, according to footage played in the courtroom in his murder trial.

The prosecution played videos that showed Fields stop his car and reverse up a hill before commencing his deadly assault on counter-protesters who were singing and celebrating after city officials had ordered the far-right demonstrators to leave.

In order to build their case of a pre-meditated attack, prosecutors presented a text Fields sent to his mother before departing for the rally after she had asked him to be careful.

"We’re not the one (sic) who need to be careful," he replied, alongside a photo of Nazi leader Adolf Hitler, whom he has long admired.

They also showed the jury two Instagram posts Fields uploaded in May last year that depicted a car ramming into a group of protesters, arguing that he ultimately chose to live out that fantasy when the opportunity arose three months later.