Ben Raymond, 32, had been convicted of remaining a member of the organisation after it was banned by the government in 2016.
He was also found guilty of two counts of possessing terrorist documents following a trial at Bristol Crown Court.
Raymond, who has a partner and baby daughter, waved from the dock as he was sent down on Friday.
Judge Christopher Parker QC said he was the “principal propagandist” for National Action, both before and after the ban.
The judge said Raymond sat “at the centre of the web” as the group split into regional factions under new names, in an attempt to evade the ban.
“In the shadows of the internet you continued to offer guidance to regional National Action organisations on tactics, security, organisation but most importantly propaganda,” he told the defendant.
“From the centre of that web you intended just as much as other associates that National Action should survive following proscription.”
Raymond denied all offences, but refused to give evidence during his trial and was convicted of membership of National Action and possessing the manifesto written by Norway shooter Anders Breivik and a manual on making explosive detonators.
He was given an eight-year prison sentence and a two-year extended period on licence. After release, he will be subject to terrorist notification requirements.
Prosecutors likened Raymond to a modern Joseph Goebbels and said he created “sick and disturbing” material, including posters glorifying terror attacks and Adolf Hitler, from his flat above a dog grooming salon in Swansea.
He wrote a book, called Attack, that vowed to “continue the battle for the final victory of our race”.
“We are done mincing words, now we need something to fan the flames,” he wrote. “We are the faithful soldiers of the National Socialist idea.”
Judge Parker said Raymond’s role as principal propagandist for National Action was “highly significant”.
He told the court that Raymond had “encouraged and promoted acts of extreme violence, pushing others forward to do your will while remaining off stage”.
“It was intended that the documents produced by you would be used to create instability within society, hatred between white people and other ethnic groups and ultimately create racial violence on which National Action could capitalise,” the judge added.
“You intended that the material should be used to recruit new members, specifically new young members … those young people were at risk of being groomed by your behaviour into committing acts of extreme racial violence.”
The court heard that Raymond was “an international neo-Nazi terrorist” who coined the term “white jihad” and forged links with groups including Atomwaffen Division in the US.
An internal National Action document detailing the group’s structure shortly before the ban named Raymond as the third-most senior member, and an “advisor/diplomat/intermediary”.
It gave him responsibility for areas including strategy, propaganda and legal issues.
After National Action was banned as a terrorist group on 16 December 2016, Raymond remained in online chat groups with his fellow neo-Nazis and attended the trials of those later prosecuted for continued membership.
The Independent previously revealed that he had written a guide for far-right extremists wanting to avoid prosecution, months before he was charged.
In a lengthy thread published on Twitter in January, Raymond offered advice based on his own experience “as a survivor” and urged readers to “follow the above steps as I did”.
He gave a separate six-page guide “prepared as evidence or criminal defence” to National Action members in a previous trial. They were all convicted.
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