The 1995 Srebrenica genocide will in future be marked around the world on July 11, following a vote by United Nations General Assembly in New York on Thursday.
The "International Day of Reflection and Commemoration" for the 8,000 Bosnian Muslims who were massacred was sponsored by Germany and Rwanda but encountered opposition from Serbia and other countries.
The day is to be officially marked from next year, 40 years after the event.
"Our initiative is about honouring the memory of the victims and supporting the survivors who continue to live with the scars of that fateful time," German ambassador Antje Leendertse said.
The resolution condemns without reservation any denial of the Srebrenica genocide as a historical event along with actions glorifying those convicted of war crimes, crimes against humanity and genocide by international courts, including those responsible for the Srebrenica genocide.
The outcome of the vote did not match expectations, with just 84 member countries in favour and 19 against, with 68 abstentions. Virtually all Balkan countries voted in favour.
China, Russia and Hungary joined Serbia in opposing the resolution. The Serbian delegation argued that it would serve to divide the region and establish a hierarchy among the victims of the war.