A court heard that Alice Cutter, 23, sported “his-and-hers swastika knitwear” with her former fiance Mark Jones – a senior figure in the banned terrorist group.
Prosecutors said the comments Cutter made about Jews, including violent fantasies of murder and ethnic cleansing, were “some of the most shocking in the case”.
She entered National Action’s “Miss Hitler 2016” competition, which was a publicity stunt to attract more members, under the name Buchenwald Princess.
It referenced a German concentration camp, where her boyfriend had performed a Hitler salute in an execution chamber the month before.
Cutter also attended National Action meetings and protests and was connected with key figures in the terrorist group including de-facto leader Christopher Lythgoe.
Jurors were shown photos of Cutter posing with what looked like an automatic rifle and knives, including blades emblazoned with Nazi symbols.
“I've gone from hanging around with humourless libtards to meeting intelligent young people who wear all black just like me,” she wrote in her “Miss Hitler” entry.
“Sacrifice is inevitable in life, so why not make the 'sacrifice' of a comfortable and ignorant life for the greater good.”
Cutter was convicted of membership of a proscribed organisation alongside Jones, 25, Garry Jack, 24, and Connor Scothern, 19, following a retrial.
Addressing the four, Judge Paul Farrer QC said a date for their sentencing would be fixed in due course.
Birmingham Crown Court heard that co-defendant Daniel Ward pleaded guilty to membership during their first trial, which ended with a hung jury last year.
Prosecutor Barnaby Jameson QC said they were part of a “fellowship of hate” who continued to further National Action’s aims after it was banned as a terrorist group in December 2016.
He said the “tiny, secretive group of die-hard neo-Nazis” were prepared to achieve their goals with terrorism, including the ethnic cleansing of Jews, black people, Asians, gays and liberals.
“The ultimate aim of the group was all-out race war,” Mr Jameson said. “Members of National Action were equipping themselves with weapons and the ability to produce explosives.”
After the neo-Nazi group was banned, Jones was one of the senior figures who received instructions from Lythgoe that National Action was “just shedding one skin for another” and would continue underground.
It fragmented into regional cells, and successor groups called Scottish Dawn and NS131 that were later banned by the government.
The defendants were in a chat group set up the following February called the “triple K mafia”, in reference to the Ku Klux Klan, where National Action members from across the midlands and Yorkshire exchanged violent posts.
Jones, described as a “die-hard” member in court, was a leading figure with connections to the group’s leadership and international neo-Nazi groups.
One of his contacts was Brandon Clint Russell, an American extremist who founded Atomwaffen Division and was later jailed for explosives offences.
In December 2017, Jones travelled to meet members of the Azov Battalion militia in Ukraine and he had been messaging a member of Lithuanian nationalist organisation Skydas.
The court heard that he was a regional organiser in London before meeting Cutter and moving to West Yorkshire to live with her in 2017.
Jones, a former British National Party (BNP) member who went by the name “Granddaddy Terror” and “Mr Angry” in chat groups, attended numerous National Action demonstrations and flew to Germany with co-founder Alex Davies in April 2016.
The pair were photographed in the execution room of Buchenwald performing a Hitler salute and holding a National Action flag.
Jones met new National Action recruits and created neo-Nazi artwork for the group, as well as Scottish Dawn and NS131.
The court heard that Jones was also photographed conducting target practice with a crossbow and assault rifle, and purchased knives and posed with them at the home he shared with Cutter.
During searches, police uncovered National Action propaganda, Nazi paraphernalia, knuckle dusters, knives, a catapult, Nazi books and Swastika earrings and scarves.
Cutter cried in the dock as the court heard that Jones had cheated on her with a 16-year-old student he was attempting to recruit, and the couple broke up during the trial.
In her evidence, Cutter told jurors she had removed the engagement ring Jones had given her when he proposed in Yorkshire over the infidelity.
Unknown to the jury, Cutter – who styled herself to other members as a “fashy princess” – also gained a romantic admirer who sent a love letter via the court during her first trial.
The pair were in the Midlands cell of National Action alongside Jack, who joined in 2016 and was described as an “out-and-out fanatic” in court.
He was previously convicted of stirring up racial hatred with a neo-Nazi stickering campaign at Aston University in Birmingham, and continued meeting members after the ban.
The youngest defendant, Scothern, practised Islam from the age of 12, then was drawn to communism before settling on National Action in his mid-teens.
The court heard that he joined demonstrations, including one that saw him make a Hitler salute at a war memorial, and downloaded a recipe for making Molotov cocktails.
In September 2017, mass arrests sparked instructions from a senior member who was jailed in a separate trial to delete messages and burn memorabilia linking them to the group.
But the four defendants and Ward were arrested on 5 September 2018 and charged with continued membership after the ban, which they denied.
Jones, Scothern and Jack claimed they quit National Action when it was banned in December 2016, while Cutter denied ever joining the group and claimed she would not have been admitted as a woman.
The case brings the total number of National Action supporters convicted of membership to 15, while several others have been jailed for other offences including plotting to kill an MP and making a pipe bomb.
Det Ch Supt Kenny Bell, head of the West Midlands Police Counter Terrorism Unit, said the defendants were a “significant part of the network”.
“Clearly the convictions are a significant disruption of National Action but I don’t take for one minute for granted the ongoing challenge,” he told The Independent.
“We’re beginning to shine a light on right-wing terrorism and some of the depraved views people are spouting. I will not be resting on my laurels over this threat.”
Jones and Cutter, both of Sowerby Bridge near Halifax, Jack, of Birmingham, and Scothern, of Nottingham, will all be sentenced at a later date.
UPDATE: This piece has been amended to clarify that Mark Jones was described in court as a “die- hard” member of National Action, rather than the BNP. Jones was also described in court as a leading figure with connections to National Action's leadership and international neo-Nazi groups.