Reddit co-founder Alexis Ohanian has resigned from the company's board asking the tech firm to replace him with a black candidate.
The move follows days of protests in America against racism and police brutality sparked by the death of George Floyd.
The tech entrepreneur has also pledged to use future gains on his Reddit stock to serve the black community.
Ohanian, who is married to black tennis champion Serena Williams, said in a video statement on Twitter that he was doing it "as a father who needs to be able to answer his black daughter when she asks: 'What did you do?'"
Ohanian founded social media platform Reddit 15 years ago with college friends Aaron Swartz and Steve Huffman.
He has now pledged to donate £800,000 ($1m) to Know Your Rights Camp, a non-profit started by former NFL quarterback Colin Kaepernick.
"I believe resignation can actually be an act of leadership from people in power right now," he said in an online video.
"To everyone fighting to fix our broken nation: do not stop," he added.
Ohanian stepped down from daily duties in 2018 but retained a seat on the company's board until now.
Reddit promoted its first female board member, Porter Gale, last year but the website has come under fire for hosting forums promoting racist content.
The company has banned groups like r/blackpeoplehate and alt-right r/MillionDollarExtreme and "quarantined" pro-Trump forum, r/TheDonald, making sure its content does not appear in website searches or recommendations.
Earlier this week, several popular Reddit forums switched their access rights to private, or banned new posts entirely, to protest against the company's hate speech policies.
Meanwhile Ellen K Pao, former Reddit chief executive, criticised her former employer in a tweet: "You don't get to say [Black Lives Matter] when Reddit nurtures and monetizes white supremacy and hate all day long."