The 26-year-old UN Women Global Goodwill Ambassador was pictured with her mouth open as if she was chanting along in solidarity with the crowds.
At one point Emma was joined by Angela Davis, 72, the renowned political activist and scholar.
Although she did not speak out about President Trump specifically, Emma shared lots of inspirational messages posted by other women on Twitter throughout the day.
The Harry Potter actress was just one of many A-list stars to demonstrate in the US capital of Washington DC.
Emma Watson joined thousands of protestors at the Women's March in Washington DC
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Emma stood among the crowds as they chanted against President Donald Trump
Emma was joined by renowned political activist and scholar, Angela Davis
Scarlett Johansson, 32, Madonna, 58, and Charlize Theron, 41, were also in full attendance in Washington, with Scarlett and Madonna both making impassioned speeches.
"I didn't vote for you but I want to be able to support you. But first I ask that you support me," she told the 70-year-old.
"Support my sister, support my mother, support my best friend and all of our girlfriends. Support the men and women here today that are anxiously awaiting to see how your next moves may drastically affect their lives," Scarlett continued.
Scarlett Johansson addressed President Trump directly at the Women's March in the US capital
Emma Watson: From child actress to international activist
Fri, April 15, 2016
Emma Watson rose to fame in Harry Potter as Hermione Grainger and here are some of her very best pictures
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Emma Watson from child actress to international activist
Over on the west coast, Jane Fonda, 79, and Miley Cyrus, 24, championed the fight on the streets of Los Angeles, with Jane holding a placard which read: "Rise against the predator in chief."
In the UK, singing stars Lily Allen, 31, and Charlotte Church, 30, took to the streets of London and Cardiff respectively.