Thomas Mair, 53, shot Cox three times and repeatedly stabbed the 41-year-old mother of two young children in her northern English electoral district.
During the attack on June 16, he shouted "Britain first" and "Keep Britain independent" his trial heard, and when arrested he told officers he was a political activist.
Her murder shocked Britain, elicited condolences from leaders around the world and led to the suspension for several days of campaigning ahead of the EU vote which had become increasingly ugly and laced with personal recriminations.
Mair, slight of build and balding with a gray goatee beard, had refused to enter a plea or speak in his defense at the Old Bailey trial, which was treated as a terrorism case.
He asked to make a statement only after the jury unanimously returned a guilty verdict but judge Alan Wilkie refused.
"You are no patriot," Wilkie told him. "By your actions you have betrayed the quintessence of our country: its adherence to parliamentary democracy."
He added: "It is clear ... that your inspiration is not love of country or your fellow citizens, it is an admiration for Nazism and similar anti-democratic white supremacist creeds."
Mair, who had no criminal record, was also convicted of grievous bodily harm after he stabbed a 77-year-old man who had gone to Cox's aid during the attack.
Cox had only been in parliament for little more than a year, easily winning the seat for the opposition Labour party in the area where she grew up.
Mair's neighbors said he had lived in a unremarkable semi-detached house in Birstall, West Yorkshire, for 20 years, that he was a loner who spent much of his time in his garden and would occasionally mow their lawns for them.
He was "very quiet, very shy" neighbor Katie Greene told the court. She said she didn't see him have any visitors. Other witnesses said he did not talk much or make eye contact.
Police pictures following a search showed a sparsely furnished neat house with barely any food in the kitchen and single beds in the bedrooms.
But there were clear signs of his far-right leanings.
On top of a bookcase in one of the bedrooms, detectives found a Third Reich eagle ornament with a swastika on it while on neatly organized shelves were dozens of books about German military history, Nazi race theory and white supremacism.
An analysis of his internet usage on computers in local libraries also showed his obsession with the far right.
In the days and months before the attack, he had read articles about the extreme right-wing British National Party, the Ku Klux Klan and Dylann Roof, the man accused of killing nine black parishioners at a church in Charleston, South Carolina.
He had also looked up the Wikipedia entry for Ian Gow, the last British lawmaker to have been killed before Cox, in 1990.
Speaking after the case, Cox's husband Brendan called the killing an act of terrorism.
"To the person who did this, we have nothing but pity that his life was devoid of love and consumed with hatred that this became his desperate and cowardly attempt to find meaning," he said in a statement.
"The killing of Jo was a political act, an act of terrorism," he added.