Thomas Mair was found guilty of murder and of grievous bodily harm with intent, possession of a firearm with intent to commit an indictable offense and possession of an offensive weapon.
The Labour MP was stabbed and shot by Mair, days before Britain voted on whether to remain in the European Union -- Cox, 41, was a prominent supporter of the "Remain" campaign.
The judge, Mr Justice Wilkie, sentenced Mair to a whole-life term. "You are no patriot," he told Mair. "By your actions, you have betrayed the quintessence of our country, its adherence to parliamentary democracy."
Sue Hemming, Head of Special Crime and Counter Terrorism at the Crown Prosecution Service, said Mair's premeditated crimes were "motivated by hate ... nothing less than acts of terrorism designed to advance his twisted ideology."
Seen as a rising star of British politics and respected across the political spectrum, Cox, who had two children, campaigned to keep the UK in the EU, celebrated diversity, championed the rights of immigrants and was an advocate of women's and children's issues.
The court heard that Mair, a Nazi sympathizer, stabbed her, shot her once in the head and once in the chest with a rifle and then stabbed her again with a dagger.
His victim cried out: "Let him hurt me, don't let him hurt you," and despite the efforts of a bystander and paramedics she died later, according to news agency CourtNewsUK.
At his home at Lowood Lane in Birstall, police found an extensive collection of Nazi memorabilia and books, a dossier on Cox; and at his local library they found evidence of Internet searches for extreme right wing material and the gun he planned to use, the agency reported.
No evidence was offered on his behalf, and his barrister Russell Flint QC made only a very short speech saying Mair's fate was in the hands of the jury, the agency said.
Politician a 'bright star'
Cox's death drew tributes from all sides, with the then Conservative Prime Minister David Cameron telling lawmakers: "She had a huge heart. She was a very compassionate, caring MP. She was a bright star -- no doubt about it." He also praised her "great track record of caring about refugees."
Jeremy Corbyn, leader of the opposition Labour Party, added: "We have lost one of our own and our society as a whole has lost one of our very best
. Jo Cox didn't just believe in loving her neighbor, she believed in loving her neighbor's neighbor."
After the verdict was announced, Corbyn posted on Twitter: "The single biggest tribute we can pay to Jo Cox will be to confront those who wish to promote the hatred and division that led to her murder."
Her husband Brendan said Cox "lit up our lives" and called for unity to ensure that "those ... who seek to divide us will face an unassailable wall of British tolerance."
Before the trial, the widower said Cox had become increasingly worried that politics was getting more extreme and "too tribal."
"She had strong political views and I believe she was killed because of those views
," he said.
Cox was elected to the British Parliament in May 2015
and in her maiden speech spoke of how British communities had been enhanced by immigration.
"While we celebrate our diversity, what surprises me time and time again as I travel around the constituency is that we are far more united and have far more in common with each other than things that divide us," she told fellow lawmakers.
'Brave eye witnesses'
Cox was killed by Mair outside a meeting with her constituents in Birstall, West Yorkshire.
At an earlier hearing, prosecutor David Cawthorne said Mair also stabbed 78-year-old passer-by Bernard Carter-Kenny who scrambled out of his vehicle to help the MP. He suffered a serious abdomen injury.
Carter-Kenny was too ill to attend the Old Bailey to give evidence, but told the court in a statement that he tried to jump on Mair's back and "take him down," according to CourtNewsUK.
The court heard that unarmed police officers tackled Mair, who told them: "It's me. I'm a political activist," the agency said.
Sue Hemming, speaking on behalf of the CPS, praised the actions of "several people [who] courageously intervened to try and save Ms Cox," and of the "brave eye witnesses" who spoke out at the trial.
White supremacist links
After the attack, one of Mair's neighbors, Diana Peters, told CNN that the assailant was "meek and mild" but though helpful "kept himself to himself."
But the US-based Southern Poverty Law Center published what it said were documents showing that he had a history of purchasing material from the National Alliance
-- a white supremacist organization based in the US -- and had a subscription to one of its magazines.
He also subscribed to a pro-apartheid group's magazine in the 1980s, the magazine's editor told CNN.
Mair was handed a whole life sentence, which means he can only ever be released upon the orders of the UK Home Secretary.
Judge scathing in his summary
In his sentencing remarks,
the judge, Justice Wilkie, called Cox a patriot and praised her selfless concern for others -- describing her as passionate, openhearted, inclusive and generous.
He told Mair: "You are no patriot. By your actions you have betrayed the quintessence of our country, its adherence to parliamentary democracy.
"You have not even had the courage to admit and acknowledge what you did."
Family celebrates Jo Cox's life
After the verdict, Jo Cox's family released an impact statement
in which they said they had no interest in the perpetrator.
"We feel nothing but pity for him; that his life was so devoid of love that his only way of finding meaning was to attack a defenseless woman who represented the best of our country in an act of supreme cowardice. Cowardice that has continued throughout this trial."
The statement celebrated the work of the MP and her skills as a mother, saying: "Jo is no longer with us, but her love, her example and her values live on. For the rest of our lives we will not lament how unlucky we were to have her taken from us, but how unbelievably lucky we were to have her in our lives for so long.
"As a much-loved friend, daughter, sister, auntie, wife and mum, Jo lit up our lives. And she still does."