The United Nations General Assembly requested the opinion nearly two years ago. It is scheduled for release at 3pm local time (13:00GMT).
Serbia lost control of Kosovo in 1999 following a Nato bombing campaign intended to stop the killing of ethnic Albanians. Kosovo declared independence nine years later.
Boris Tadic, the Serbian president, warned that a ruling in favour of statehood would set a dangerous precedent.
"If the International Court of Justice sets a new principle, it would trigger a process that would create several new countries and destabilise numerous regions in the world," Tadic said.
Nearly 70 countries have already recognised Kosovo as an independent state, including the United States and 22 of the 27 European Union members.
Joe Biden, the US vice-president, met with Thaci on Wednesday and said that he expected the court to endorse Kosovo's independence.
"The vice-president reaffirmed the United States' full support for an independent, democratic, whole and multi-ethnic Kosovo," the White House said in a statement.
Serbian officials, meanwhile, have said that they want to continue negotiations on the status of Kosovo after the ICJ verdict.
Vuk Jeremic, the Serbian foreign minister, called on Wednesday for a "compromise solution on the future status of Kosovo".
But Kosovar officials have ruled out any further status negotiations with Belgrade.
In Belgrade, Al Jazeera's correspondent Aljosa Milenkovic said the media were split on the issue.
"Fifty per cent are saying that they have reliable sources claiming Serbia's victory in the ICJ ruling, while the other half are claiming they have credible sources that say Kosovo will win."
But Barnaby Phillips, Al Jazeera's correspondent in Pristina, Kosovo, said regardless of Thursday's ruling the positions of Kosovo and Serbia would remain "entrenched".
"Serbia basically says it will never recognise Kosovo as a sovereign country and the government here in Pristina is saying to Belgrade 'Get real, you're not coming back, independence is a fact on the ground and the people here are living here everyday'."
Serbia considers Kosovo to be its southern-most province and the cradle of the Serb nation, but its population is predominantly ethnic Albanian.
Nato peacekeepers in Kosovo have said they do not expect any violence after the ruling is issued.
"On the field we have no indications about nervousness, about any upcoming threat," General Markus Bentler, the German commander of the Nato force in the region, said.