Babic, 50, was serving a 13-year prison term for crimes against humanity, after admitting persecuting the non-Serb population in Croatia's Krajina region. He was a key ally of former Yugoslav President Slobodan Milosevic but later testified against him at the tribunal.
He was found dead on Sunday evening, the tribunal said in a statement. "The Dutch authorities were called immediately. After conducting an investigation, they confirmed that the cause of death was suicide," the statement said. It did not say how Babic had killed himself.
A spokeswoman for the tribunal, Alexandra Milenov, told the BBC that, like all detainees, Mr Babic was subject to regular monitoring. "He was checked at six o'clock and everything was found to be all right and at six-thirty when he was checked again his body was found." A tribunal judge has opened an inquiry.
Babic feared retribution for testifying against Slobodan Milosevic in 2002, and had been had been serving his sentence at a secret location, at his own request. He was brought back to The Hague last month to testify in the trial of Milan Martic, his successor as Croatian Serb leader.
Babic was president of the self-declared breakaway Krajina Serb republic, covering about one-third of Croatian territory, after Croatia declared independence from Yugoslavia in 1991.
He was jailed in 2004 for crimes committed during Croatia's 1991-1995 war. In return for his guilty plea, prosecutors dropped four other charges of murder, cruelty and the wanton destruction of villages.
Last year, judges rejected an appeal against his lengthy sentence. A dentist by profession, Mr Babic had expressed shame and remorse over his actions in Krajina. It is the second time a detainee in The Hague has committed suicide. The first was Slavko Dokmanovic, another Croatian Serb leader, in 1998.
Güncelleme Tarihi: 20 Eylül 2018, 18:16