Charlotte Church has said austerity is "unethical, unfair and unnecessary" as she joined crowds at the front of tpday's march in London.
Brandishing an End Austerity Now placard, she said she was proud to join demonstrators - posing for photos with some.
She said: "I'm here today in a show of solidarity with everyone here - it is a massive turnout - everybody who thinks that austerity isn't the only way and thinks it is essentially unethical, unfair and unnecessary.
"I'm immensely proud to be here. I think this is a brilliant movement and it is for the common good. We are here to make a stand."
Singer Charlotte Church has attacked the sexism of the "juvenile" male-dominated music industry, which she said was increasingly creating and promoting "child-like" sex objects.
Delivering the John Peel Lecture at the annual Radio Festival in Salford, she said radio executives needed to take some of the responsibility for playing artists who relied on "soft porn" to boost their profile.
Church, 27, said women were being "coerced" into sexual roles to cling on to their careers and she classified women who were overtly using sexual imagery to boost their careers such as Rihanna and Miley Cyrus as "unattainable sexbots".
"The culture of demeaning women in pop music is so ingrained as to become routine, from the way they are dealt with by management and labels, to the way they are presented to the public," she said.
Church's speech is to be broadcast at midnight tonight by BBC Radio 6 Music.
Charlotte Church has accepted substantial undisclosed High Court libel damages over a claim in The People that she proposed to her boyfriend during a boozy pub karaoke night.