Thomas Mair has been jailed for life after being found guilty of the murder of Labour MP Jo Cox.
The 53-year-old shot and stabbed to death the mother-of-two in Birstall, West Yorkshire, on 16 June, a week before the EU referendum vote.
Mair shouted "Britain First" in the attack, but the judge said the true "patriot" was Mrs Cox, not Mair.
Prosecutors said Mair was motivated by hate and his crimes were "nothing less than acts of terrorism".
Mair was also found guilty of having a firearm with intent, causing grievous bodily harm with intent to 78-year-old Bernard Kenny, who tried to help the MP, and having an offensive weapon, namely a dagger.
Mair, dressed in a dark suit and blue tie, remained impassive as the verdicts were read out, after one hour of deliberations.
He had not entered a plea and chose not to give evidence in his defence at the trial.
Before sentencing, Mair asked to speak to the courtroom but the judge declined, saying he had already had an opportunity.
At court
Daniela Relph, BBC News correspondent
The jury took just one hour and 36 minutes to reach its verdicts. Every seat in courtroom eight of the Old Bailey was filled as the jury foreman stood to deliver the guilty verdicts.
From Mair there was no reaction. He had maintained his silence throughout the trial and during every police interview.
As the verdicts were delivered, Jo Cox's family smiled. Her sister, Kim, held her mother's hand. Then Jo Cox's husband read a victim impact statement.
Standing in the witness box, in front of the man who murdered his wife, Brendan Cox told Mair that he pitied him because his life was devoid of love and consumed by hatred. It was a highly charged moment.
The Cox family watched as Mair was led away, in silence, to begin his life sentence.
Mrs Cox's husband Brendan said he was not there for "retribution" and felt "nothing but pity for" Mair, in a statement read out to the Old Bailey.
Speaking outside court, he said his wife's killing was an incompetent and self-defeating act of terrorism that was driven by hatred but instead created an outpouring of love.
His family would not respond to hatred with hatred, he said, and Jo's ideas and values would live on in her children, and family.
In sentencing, Judge Mr Justice Wilkie described Mrs Cox as a wonderful mother, sister, daughter and companion, with a generosity of spirit that was apparent even when faced with a violent death.
Mair's inspiration was not love of country but admiration for Nazism, the judge said, which was a betrayal of our parents' generation's huge sacrifices during World War II.
He said Mair had not the courage to acknowledge what he did and forced Mrs Cox's family to relive the events.
Judge Mr Justice Wilkie said the murder was carried out to advance a political cause of violent white supremacism, associated with Nazism.
He said the aggravating feature was the premeditation and planning over weeks, in which he researched his intended victim, the past assassination of a serving MP and matricide, knowing Mrs Cox was the mother of young children.
The judge sentenced Mair to life imprisonment, with a whole life term.
He said he had concluded that the offence was so exceptional that Mair could only be released by the home secretary.
Mrs Cox's parents, Jean and Gordon Leadbeater, and her sister, Kim, were also in court for the verdicts.
Kim Leadbeater said her family were relieved that the process was over after a difficult few months.
"There may have been one act of extreme cowardice on that day, but there were acts of extreme bravery.
"I, for one, will not be beaten by what has happened and I know I am not alone," she said.
Home Secretary Amber Rudd said the "shocking and senseless murder" of Mrs Cox was "an attack on all of us and the values we share of democracy and tolerance".
"As home secretary, I am determined that we challenge extremism in all its forms including the evil of far right extremism and the terrible damage it can cause to individuals, families and communities," she said.
The Crown Prosecution Service said in a statement: "Mair has offered no explanation for his actions but the prosecution was able to demonstrate that, motivated by hate, his pre-meditated crimes were nothing less than acts of terrorism designed to advance his twisted ideology."
The CPS said it worked closely with police to build a strong case, and commended a number of "brave" eye witnesses who gave evidence.
Det Supt Nick Wallen, of West Yorkshire Police, said Mair was a "cold-blooded killer" who lived a solitary lifestyle, with no social circle and had never come to the notice of the police before.
He said nothing could ever excuse the evil and the horror that he brought to the small town of Birstall.
