A war crimes appeal hearing was halted just after the verdict was announced on Wednesday, when the defendant claimed to have taken poison.
Footage from the International Criminal Tribunal at at The Hague showed Slobodan Praljak, a former Bosnian Croat general, drinking from a small bottle before his lawyer claims he has taken poison.
The judge is then heard immediately suspending proceedings.
Praljak, a former assistant defense minister of Croatia and at the same time a commander of the Croatian Defense Council, was appealing a jail term of 20 years in prison.
He was one of six former Bosnian Croat leaders found guilty of crimes against humanity and war crimes, including the rape and murder of Bosnian Muslims, in 2013.
The nature of the substance ingested by Praljak was not immediately clear .