Facebook, Twitter, YouTube and Microsoft made the pledge in a code of conduct worked out with the European Commission, the EU's executive.
"The recent terror attacks have reminded us of the urgent need to address illegal online hate speech. Social media is unfortunately one of the tools that terrorist groups use to radicalize young people," EU Justice Commissioner Vera Jourova said in a statement.
The code of conduct includes several commitments by the internet giants, including a promise to "review the majority of valid notifications for removal of illegal hate speech in less than 24 hours and remove or disable access to such content, if necessary."
"We remain committed to letting the tweets flow. However, there is a clear distinction between freedom of expression and conduct that incites violence and hate," Twitter representative Karen White said.
Facebook official Monika Bickert called on users to take advantage of the website's reporting tools to flag problematic content, promising that teams of employees around the world "review these reports around the clock and take swift action."
The four companies also pledged to educate their users about forbidden content, train their staff on societal developments and share best practices with other social media firms.
However, the code of conduct faced criticism Tuesday from European Digital Rights, an association of digital civil rights groups.
The advocacy association argued that civil society had been excluded from negotiations on the code of conduct, which it says will leave internet companies in the lead when it comes to policing controversial speech online, rather than law enforcement.
This creates "serious risks for freedom of expression, as legal but controversial content may well be deleted as a result of this voluntary and unaccountable takedown mechanism," the group said in a statement.
©2016 Deutsche Presse-Agentur GmbH (Hamburg, Germany) Distributed by Tribune Content Agency, LLC.
