The People's March - previously known as the Women's March - has taken place every year since 2017.
A coalition of groups organised the movement with the stated aim of confronting "Trumpism", according to its website. Smaller protests against Trump were held in New York City and on the other side of the country in Seattle.
The rallies coincide with Trump's arrival to the nation's capital for a series of weekend events in the lead-up to his swearing-in ceremony on Monday.
The groups behind the march are described on its website as holding "intersecting identities" and having "varied issue-based interests" with different causes such as climate change, immigration and women's rights.
BBC