As part of a deal with prosecutors, Miroslav Deronjic, 49, confessed to a single charge of persecution for ordering the destruction of the Muslim village of Glogova in Bosnia on 9 May 1992, in which 65 civilians were killed.
Reading a summary of the judgement, presiding Judge Wolfgang Schomburg said the tribunal sought to "balance the extreme gravity of the crimes against his contribution to coming closer to the truth" about war crimes in the former Yugoslavia.
In exchange for his plea and testimony against Milosevic and others, which described first-hand how the process of "ethnic cleansing" of Muslims took place in Bosnia, prosecutors dropped five other charges against Deronjic and recommended a 10-year prison sentence.
'Burn it down'
In several previous cases, the judges ignored recommendations for relatively light sentences.
Captain Momir Nikolic, who helped with logistics at Srebrenica, was imprisoned for 27 years despite a request for 15-20 years by the prosecution in a plea bargain.
Deronjic was the top wartime authority in the eastern Bosnian city of Bratunac.
Thousands of Bosnian men and
boys were massacred at Srebrenica
As such, he admitted giving the order "to attack the undefended and disarmed village of Glogova, burn it down, and forcibly displace its Bosnian Muslim residents, taking into account the substantial likelihood that some of them would be killed", Schomburg said.
Deronjic then reported back to the parliament of the breakaway Bosnian Serb republic, where he was applauded by the Bosnian Serbs' top political leader Radovan Karadzic and top general Ratko Mladic.
At Milosevic's trial in November, Deronjic said he met a bureaucrat in Milosevic's own office building in Belgrade to arrange a weapons shipment across the Serbia-Bosnia border in 1991, suggesting close cooperation between Serbs in Bosnia and Serbia.
Deronjic was one of three high-profile suspects who pleaded guilty last year and gave evidence about ethnic cleansing, including the 1995 massacre at Srebrenica, Bosnia, where over seven thousand Muslim men and boys were systematically killed.
In Deronjic's testimony about Srebrenica, he said the top Bosnian Serb leadership not only knew about, but also planned and ordered the massacre.
(The Muslims of Srebrenica) "need to be killed ... everything you can get your hands on"
former Bosnian Serb politician
Deronjic said Karadzic told him personally on July 9, 1995, that the Muslims of Srebrenica "need to be killed ... everything you can get your hands on."
Two days later the massacre began, under Mladic's supervision.
Karadzic and Mladic are the tribunals' most-wanted fugitives. Both are indicted for genocide for Srebrenica.
Milosevic's trial on 66 counts of war crimes, which began two years ago, is in recess until June, when Milosevic will open his defence.
The prosecution rested its case last month.