Vasiljkovic, who has been accused of three counts of war crimes in 1991 and 1993, will be handed over to Croatia unless the Australian Government intervenes, according to ABC news.
In November 2012, former federal justice minister Jason Clare approved the Australian citizen's extradition and the Federal Court backed that ruling in December.
Vasiljkovic applied for leave to appeal in the High Court, arguing the approval was improper based on procedural fairness and sections of the Geneva convention. However, the High Court has ruled the appeal would be unlikely to succeed and has refused leave to appeal.
The only thing now standing between him and extradition is an about face by current Justice Minister Michael Keenan, ABC news reported.
Vasiljkovic, 60, also known as Daniel Snedden, has been in prison for nine years — but freed briefly for an eight-month period — since his arrest as his case progressed through the courts.
In 2013 Vasiljkovic managed to prolonge his extradition to Croatia, arguing the approval was improper based on procedural fairness and sections of the Geneva convention.
Vasiljkovic is accused of leading a paramilitary unit of ethnic Serbs who were involved in a conflict with the Croatian armed forces.
His men are accused of committing war crimes, including torture, murder and conducting mock executions.
Vasiljkovic is alleged to have ordered paramilitary units to fire on a church, a school and homes, while his soldiers have been accused of looting homes after the attack.
Croatia originally applied to extradite him in 2006.