The death cast a pall over the last case at the groundbreaking International Criminal Tribunal for the former Yugoslavia.
Praljak was among six former leaders of the wartime "Croat Republic of Herzeg-Bosnia (Herceg-Bosna)" - whose guilty verdicts were confirmed today by the Appeals Chamber. During this time Mr Praljak, a senior commander in the Bosnian Croat forces, was found to have taken no serious action to stop his soldiers from rounding up Muslims. "I reject the verdict with disdain", he shouted.
He then drank from what appeared to be a small vial, ignoring calls from the judge to sit down.
The hearing was quickly suspended as Praljak's lawyer interjected: "My client says he has taken poison".
By that point, Praljak was out of shot of the cameras, but a security guard told the media that Praljak was still alive. He could not confirm what was in the bottle.
He was facing the United Nation (UN) tribunal in The Hague.
He told the judge: "I have taken poison".
"Slobodan Praljak is not a war criminal".
"It is a humiliation of this institution which has existed since 1993".
The chamber acquitted the defendants on charges of crimes committed against civilians in Mostar.
Slobodan Milosevic, the former Serbian leader, died of a heart attack in his jail cell in 2006, while his own ICTY trial was underway.
But in their ruling, the judges in fact allowed part of Praljak's appeal, saying the bridge had been a legitimate military target during the conflict. But they refused to reduce his overall sentence.
The appeals judges upheld a key finding that late Croat President Franjo Tudjman was a member of a plan to create a Croat mini-state in Bosnia.
The aim of the scheme was to set up "a Croatian entity that reconstituted area borders and that facilitated the reunification of the Croatian people".
His judgement had also descended into confusion when he accused the judges of lying and had to be dragged away into a nearby room to watch the end of the proceedings. Of the 161 individuals indicted by the ICTY, the body created specifically to prosecute wartime crimes, 94 are ethnic Serbs, compared to 29 Croats, nine Albanians and nine Bosniaks.