Michael Sheen is stepping back from his acting career to fight against the rise of the "hard populist right" as an activist.
The Welsh actor said the "demagogic, fascistic" change in politics, including the election of Donald Trump, has prompted his desire to counter it.
The 47-year-old, who has appeared in the TV show Masters of Sex and dozens of films including Twilight, revealed the move in an interview in The Times magazine.
He said that through grassroots organising in his home town of Port Talbot, he will fight the rise of the "hard populist right" which has emerged in places such as the UK, the US, France and Austria.
"It means that I would work less as an actor, and possibly stop," he said."Once I'm in, I'm fully in, and this is big. It will be a big change for how people relate to me."
Sheen has already been outspoken on a number of issues including protecting the NHS and criticising potential changes to freedom of information (FOI) legislation.
He has also called for the Government to support steel workers and visited a refugee camp to speak out about the plight of Syrian children affected by war.