The count of genocide relates to a campaign of killing and mistreating non-Serbs in seven municipalities at the start of the Bosnian war in 1992.
The ruling means he now faces 11 charges, including a further charge of genocide for the Srebrenica massacre.
More than 7,500 Muslim men and boys died in the enclave in July 1995.
It was the worst atrocity in Europe since the end of World War II.
The tribunal’s decision was passed as thousands of people gathered in the Bosnian town of Srebrenica for the burial of more than 400 newly-identified victims of the 1995 massacre.
Read more at BBC.co.uk.