Former Kosovo President Hashim Thaci has been found guilty of war crimes including murder, torture and illegal detention.
He was also convicted of arbitrary illegal detention of 385 people, torture of 303 people and treatment of about 50.
In Pristina, Kosovo's capital, thousands of people watching the verdict on a big screen booed the verdict.
Former Kosovo President Hashim Thaci has been found guilty of war crimes, including murder, torture and illegal detention by the Kosovo war crimes tribunal in The Hague.
Thaci, 58, was sentenced to 25 years in prison for crimes committed as top commander of the ethnic Albanian Kosovo Liberation Army (KLA) during the territory's violent break from Serbia in the 1990s.
The tribunal said he was guilty of the murder of 96 political opponents and perceived collaborators with Serbian security forces by Kosovo Liberation Army forces during the conflict.
The court said Thaci had "actively participated in and encouraged crimes".
"The scale and nature of the crimes committed were very serious," presiding judge Charles Smith said.
"The so-called intelligence on which many of these victims were arrested, detained and killed was little more than unverified rumours. Based on that information, victims were called and described as spies and collaborators and violently treated."
The ruling was closely watched in Kosovo and Serbia, where the legacy of the 1998-99 conflict and Kosovo's 2008 declaration of independence remain a source of tension between ethnic Kosovo Albanians and Serbs.
Thaci remains a revered figure for many Kosovo Albanians, while the tribunal itself is unpopular in Kosovo.
One billboard showed the faces of the defendants, which read: "In the name of the people you are declared innocent".
Albania's Prime Minister criticised the verdict with a picture posted on social media of a circle of barbed wire across a map of Europe and one word: "Unbelievable".
Prosecutors had sought a 45-year sentence against Thaci and three other former top commanders of the KLA.
But the three-judge panel dismissed six charges of crimes against humanity.
However, they ruled that Thaci and his co-accused were part of a joint criminal enterprise, with a common plan to take control of Kosovo politics following its independence by targeting political opponents.
Thaci's lawyers had argued the accusations were unfounded, amounted to an attempt to rewrite history and there was no evidence to directly link Thaci to any of the alleged crimes..