The UN Treaty on the Prohibition of Nuclear Weapons, which was adopted in 2017, will become the first international norm outlawing the development, testing, possession and use of nuclear weapons.
UN Secretary General Antonio Guterres commended the 50 countries and saluted "the work of civil society, which has been instrumental in facilitating the negotiation and ratification of the treaty."
The pact will enter into force 90 days after it has been ratified by at least 50 countries and regions.
Honduras was the latest country to complete the ratification procedure.