Ivanovic rose to prominence after the Kosovo war in 1999, which ended with Serbian forces pulling out of the mostly Albanian-populated region.
Serbian politician Oliver Ivanovic was gunned down outside his office as he arrived for work in the Kosovar city of Mitrovica on January 16, Agence France-Presse reported.
"Unfortunately, I wish it weren't true, but doctors declared Oliver dead at 9:30 this morning, " Nebojsa Vlajic, Ivanovic's lawyer told AP by phone.
Ivanovic, 64, was gunned down in front of his party office in Mitrovica, a town bitterly divided between ethnic Serbs and Albanians, shortly after 8 a.m. (0700 GMT). That verdict was overturned and a retrial had been underway. The United Nations administered Kosovo in the years following the end of the conflict, working with Ivanovic and other Kosovo Serb politicians, even though Serbia never officially recognized Kosovo's independence.
Kosovo Prime-Minister Haradinaj condemned the criminal act, stating the Kosovo government is committed to ensure a safe environment for all its citizens.
Serbian President Aleksandar Vucic described the murder as "an act of terror" and vowed to find those responsible.
In Pristina, the Kosovo government strongly denounced the slaying, saying it considers the attack a challenge to "the rule of law and efforts to establish the rule of law in the whole of Kosovo territory".
The head of Belgrade's Office for Kosovo and Metohijam, Marko Duric, called the killing a "terrorist attack" targeting the entire Serbian people, TANJUG news agency said. Police said later no one had heard the shots, but Ivanovic's neighbor who was returning home after shopping found the wounded politician.
Ivanovic's arrest in 2014 led to protests by ethnic Serbs in Kosovo and strong objections from Belgrade, which does not recognize the independence of its former province.
Relations between Serbia and Kosovo have been tense since 2008, but in 2013 both parties agreed to participate in the EU-sponsored negotiations on normalising relations, a condition for both to progress on their way towards membership in the bloc. Kosovo fears that Serbia may be trying to annex the Serb-majority region in the north.
In 2016, Ivanović was found guilty of ordering crimes against the civilian population in 1999 during the Kosovo War.