Led by the Women's Equality Party, the Women's March London will end with a speech from founder Tanya Moodie about "the politics of fear".
Participants will be at the demonstration as a show of solidarity with women also marching in Washington on Saturday (January 21).
Party leader, Sophie Walker, said: "This year I want to lead a party and a movement of women and men who will stand strong in the face of racism, sexism, homophobia and all other kinds of discrimination.
"We must unite to protect our rights in the face of a US administration and uncertain Brexit negotiation.
"We must protest an environment in which many minorities feel threatened.
"We must build tolerance and diversity at all levels of society."
She said: "I am very proud to be joining men and women from across the country, and the world, to lead the walk across London and to mark the start of a movement for real change.
"I look forward to joining with people from across the country to show the world that we will not tolerate these attitudes any more."
The march, starting at midday at the US Embassy, will move on to Trafalgar Square through the afternoon as the rally continues.
Organisations have urged it is a "peaceful" demonstration and people should come with an "open mind and an open heart".
"What happens in America matters everywhere," said Catherine Mayer, Women's Equality co-founder and a dual US-UK national.
"It is not only the world’s biggest economy but the biggest exporter of ideas," she said.
"We will march in solidarity with women and girls in the US and across the world who face barriers to their living free and equal lives.
"We hope men and boys will join us, not only in recognition of these structural injustices but for their own sakes, because a more equal society will be better for them too."
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