When sentenced, Jack Renshaw raised his arm in an apparent Nazi salute as a supporter in the public gallery shouted “we’re with you Jack” while he was led to the cells.
The 23-year-old bought a 19-inch (48cm) Gladius knife to kill Rosie Cooper and exact revenge on a female police officer who was investigating him for child sex offences.
The plan was scuppered by whistleblower Robbie Mullen, who was at a meeting in a pub when Renshaw announced that he was going to kill Cooper in July 2017.
It came just a year after Labour MP Jo Cox was stabbed and shot by far-right extremist Thomas Mair.
Renshaw, from Skelmersdale, Lancashire, is a convicted paedophile who was jailed last June for 16 months after he groomed two underage boys online.
Jurors at Preston Crown Court had found him guilty of four counts of inciting a child to engage in sexual activity.
Renshaw set up two fake Facebook profiles and contacted the boys, aged 13 and 14, between February 2016 and January 2017.
Communicating via Facebook messenger, Renshaw boasted to the youngsters that he was rich, could give them jobs and offered one of them £300 to spend the night with him.
He also requested intimate photographs of the pair, before one of the boys reported the messages to his tutor and the police were contacted.
Renshaw also received a three-year prison sentence two months earlier when he was found guilty of stirring up racial hatred after he called for the genocide of Jewish people.
He went on to admit making preparations to kill his local MP and making a threat to kill police officer Victoria Henderson.
But he denied membership of banned extreme right-wing group National Action and a jury was discharged when they failed to reach a verdict.
Hope Not Hate chief executive Nick Lowles said Renshaw’s plot “shouldn’t have come to this” and authorities “took their eye off National Action”.
“Former National Action members are still active, successor organisations are being formed, and a threat still clearly remains,” he said.
“Too little effort has gone into understanding the mindset of those attracted into this violent, nihilistic breed of far-right terrorism, or the culture from which they emerge – or then enter.”
Sentencing Renshaw, Justice McGowan said: “Your perverted view of history and current politics has caused you to believe it right to demonise groups simply because they are different from you.”
She added: “This is a case in which only a sentence of life imprisonment can meet the appalling seriousness of your offending.”
The judge also commended MP Rosie Cooper and police officer Victoria Henderson.
“The dignity and bravery they have demonstrated show the true public spirit and public interest that motivated their work,” she said.
In a statement after the sentencing, Cooper said: “My deepest wish is that this case is the last occasion when any public servant, any politician, has their life threatened for simply doing their job.
“I believe today justice has been served. Not for me personally, but for every MP and public servant, and for our democratic way of life which affords us the privilege of free speech, without fear of violent retribution.”