As part of her role as UN Women Goodwill ambassador, the actress spoke at the launch of the #HeForShe initiative, which calls on men to fight sexism.
She said that equal opportunities between the sexes will never be reached so long as "only half of it is invited or feel welcome to participate in the conversation", going onto to note prejudices that come with being a man.
"Men - I would like to take this opportunity to extend your formal invitation," she said. "Gender equality is your issue too."
She also discussed misconceptions of feminism and how it is often associated with "man-hating".
"For the record, feminism by definition is: 'The belief that men and women should have equal rights and opportunities. It is the theory of the political, economic and social equality of the sexes,'" she said.
Her speech has attracted the approval of famous names including Joseph Gordon-Levitt and Douglas Booth, but no reaction has been as great as a letter penned by a 15-year-old boy.
An abridged version was published in The Telegraph, yet Buzzfeed has run the full letter in all its articulate, intelligent glory.
Ed Holtom felt so "disappointed" about how "how ignorant" some of the boys in his class were about feminism, following Watson's speech, that he was inspired to write down his views on gender equality.
"We’re lucky to live in a western world where women can speak out against stereotypes," he wrote. "It’s a privilege. Gender equality and feminism is not about 'man-hating' or the idea of 'female supremacy'. It is, by definition, the opposite. The definition of feminism is, 'a person who believes in the social, political and economic equality of the sexes.'
"It’s pretty simple really, and if you believe in those things, then you’re a feminist. Feminism can also be interpreted as a woman owning her sexuality, in the same way men do, wearing clothes that make her feel good about herself, or that show off her body, not for the attention of men, without being called a s**t and with freedom from the threat of rape, because she wants to."
He went on to say that other than "human genitalia" there is nothing to differentiate being masculine or feminine and that we can control whether or not gender stereotypes continue to be perpetrated.
"If we want equality, it will take more effort than paying women the same as men, or giving women equal opportunities to men," he said.
"If we really want equality we must all make an active decision to abandon phrases such as 'what it means to be masculine' and the like. If we really want equality we must try our best to ignore gender and stop competing with one another. We must stop comparing ourselves to each other, particularly other people of the same gender, because that leaves us with a feeling of insecurity and self-doubt.
"We must stop pressuring each other to fit with this stereotype which more often than not leaves us feeling repressed and unable to express ourselves. And most of all, if we really want equality, we need to stop caring. Stop caring about gender, stop caring about another person’s sexual preference, stop caring about how far someone fits in with the stereotype and stop caring, most of all, about how much we fit this stereotype, we must not let gender define us."
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