It means that being a member of the group, or inviting support for, becomes a criminal offence.
A neo-Nazi movement is to become the first far-right group to be banned under terrorism laws in the UK.
Announcing the move, Home Secretary Amber Rudd described National Action as a “racist, anti-Semitic and homophobic organisation”.
An order laid in Parliament on Monday to proscribe National Action under the Terrorism Act 2000 – making it a criminal offence to join or support it – is due to come into effect on Friday.
National Action describes itself as a “National Socialist youth organisation” and says its movement is aimed at the “broken right-wing”.
Ms Rudd said: “As Home Secretary, I am clear that the safety and security of our families, communities and country comes first.
“So today I am taking action to proscribe the neo-Nazi group National Action.
“This will mean that being a member of, or inviting support for, this organisation will be a criminal offence.
“National Action is a racist, anti-Semitic and homophobic organisation which stirs up hatred, glorifies violence and promotes a vile ideology, and I will not stand for it.
“It has absolutely no place in a Britain that works for everyone.”