In confessing his guilt on Thursday, Dragan Nikolic catalogued the horrifying crimes that were perpetuated on Muslim detainees at the Susica camp in Bosnia during the 1992-95 civil war.
Nikolic was first charged by The Hague-based International Criminal Tribunal for the Former Yugoslavia in 1994, just one year after its creation and was transferred to the war crimes court in April 2000.
Prosecutors are seeking a 15-year jail term for Nikolic, who is expected to be sentenced in November.
Nikolic had initially protested his innocence and pleaded not guilty.
According to the indictment, 8,000 Muslim civilians and non-Serbs were detained at the camp in inhumane conditions.
Guards routinely beat them and prosecutors say many of the women detainees were sexually assaulted.
Nikolic's guilty plea exempts him from a trial. The UN court will instead hold a session in November to determine whether any special circumstances related to his crimes should affect his sentencing.
Former Bosnian Serb leader Biljana Plavsic, who pleaded guilty last February to crimes against humanity during the war, is serving out an 11-year sentence in a Swedish prison.