The European Court of Human Rights is to decide whether it is a crime to deny that the mass killings of Armenians by Ottoman Turkey in 1915 was "genocide".
The landmark freedom of speech case was sparked by a Swiss court's 2007 conviction of Turkish politician Dogu Perincek after he said publicly the "Armenian genocide is a great international lie".
It gained additional attention in January when Armenia was represented by prominent human rights lawyer Amal Clooney at a hearing.
The ECHR's 17-judge Grand Chamber will announce its decision at 9:45am on Thursday (local time) at a brief public hearing expected to be attended by representatives of both the Turkish and Armenian communities.
It was not clear if Clooney, who represented Armenia as a third party in the case, would be present for the judgment.
The Swiss court in 2007 ordered Perincek, chairman of the Turkish Workers' Party, to pay a fine after finding him guilty of racial discrimination for his remarks, which he repeated on several occasions.
Turkey has always denied that the killings, which started in 1915, were a pre-meditated attempt by the then ruling Ottomans to wipe out the Armenians.
It also says only 500,000 died, not 1.5 million as claimed by Armenia.
Before the events, about two million Armenians were living in the territory of the Ottoman Empire.
More than 20 nations have so far recognised the killings as genocide, a definition supported by numerous historians but vehemently opposed by Turkey.
After his conviction, Perincek took the case to the ECHR, arguing that his freedom of speech was infringed.
A lower chamber of the ECHR, ruling in December 2013, rejected the Swiss court's conviction, saying that Perincek's remarks fell within the boundaries of free speech.
Switzerland appealed that ruling, and the case came before the ECHR's Grand Chamber.
The Swiss side argues that denying that a genocide occurred is tantamount to "accusing the Armenians of falsifying history, one of the worst forms of racial discrimination".
Perincek's lawyers and those of the Turkish government argue that there is no "general consensus" that the killings were genocide.