Organisers urged people worried about in-person participation to join in a "socially distant text-banking telethon" aimed at sending five million messages encouraging people to vote.
Marchers also paid tribute to late Supreme Court justice Ruth Bader Ginsburg - an icon for women and progressives - while protesting Mr Trump's choice of conservative judge Amy Coney Barrett to replace her.
The parade route in Washington started near the White House before heading to the US Capitol and then to the National Mall.
Some protesters were heading afterward to the Supreme Court building, where a smaller "I'm With Her" counterprotest - in Judge Barrett's favour - was scheduled.
Most marchers in Washington wore protective masks, with some dressed as Justice Ginsburg in black robes with white lace collars, and several wore the knitted pink hats made famous by the original march.
Their signs and banners underscored the broader anti-Trump message: "Trump/Pence: Out Now," read one, while others simply said, "Dump Trump."
In New York City, around 300 people gathered at Manhattan's Washington Square, many with pink hats and signs supporting Mr Trump's Democratic opponents Joe Biden and Kamala Harris or honouring Justice Ginsburg. It was one of five separate marches in the city.
Thousands of women march across the US in anti-Donald Trump rallies
"It’s really important to be here and try to encourage people to vote out Trump and his misogynistic policies, especially now, with COVID, when a lot of people are isolated," said Yvonne Shackleton, a 47-year-old working mother from near Albany, about a three-hour drive from New York City.
The Women's March website, harking back to the huge turnout for the 2017 marches, said, "We need to bring that same power and determination to 17 October to cap off Trump's presidency just the way it started - with massive, women-led resistance."
Mr Trump's support from women has dropped sharply - particularly among suburban women. He now trails Mr Biden among likely women voters by 23 points, according to a recent Washington Post/ABC News poll.