PARIS — A United Nations court on Wednesday increased the sentence of Radovan Karadzic, the former Bosnian Serb leader, from 40 years to life in prison for his role in the Bosnian war of the 1990s, reaffirming his conviction on charges of genocide, war crimes and crimes against humanity.
Both the prosecution and the defense had appealed the 2016 result of Mr. Karadzic’s trial before the United Nations Criminal Tribunal for the Former Yugoslavia, in The Hague. Mr. Karadzic, who largely acted as his own lawyer in court, had asked to be acquitted of all charges.
The prosecution sought an increase in his sentence — a largely symbolic move, because Mr. Karadzic, 70 at the time of the verdict, was unlikely to live long enough to serve out his 40-year sentence. But symbolic or not, the court’s decision on Wednesday to raise the penalty drew cheers and applause from Bosnians watching in the gallery.
The five-judge panel decided 3 to 2 that it was unreasonable for Mr. Karadzic to receive a 40-year sentence when some of his subordinates had been sentenced to life for their roles in the same atrocities, particularly the July 1995 massacre in and around the town of Srebrenica. The defendant watched calmly as the decision was delivered.
Prosecutors had asked the court for an additional genocide verdict in the case, based on events in seven Bosnian towns where tens of thousands of people were killed, but the panel rejected that request, which had been the subject of intense debate among lawyers, human rights groups and victims.
During the war, which raged from 1992 to 1995, Mr. Karadzic was the president of Republika Srpska, the region that tried to break away from Bosnia, where violence carried out by the dominant Serbs forced out much of the Croat and Muslim population.
His trial, followed by the three years of appeals, was the most important in the 23-year history of the United Nations tribunal, and was widely seen as a test of whether the modern international criminal justice system could impose accountability on wartime leaders.
The proceedings thoroughly investigated the bloodiest conflict in Europe since World War II, which tore apart Yugoslavia, ravaged several of the smaller nations that emerged from it, and left more than 100,000 people dead. Among the Balkan combatants — Serbia, Bosnia, Kosovo and Croatia — millions of people were displaced, many of them forced from their homes in campaigns of ethnic cleansing.
The tribunal has tried many figures for crimes in the wars that broke up Yugoslavia. Mr. Karadzic and Gen. Ratko Mladic, the former Bosnian Serb commander, are the most senior figures to be convicted. Slobodan Milosevic, the Serbian president whose extreme nationalism instigated and enabled the bloody conflict, died in 2006 in his cell in The Hague before the end of his trial.
The genocide charges against Mr. Karadzic dealt partly with the Srebrenica massacre, when 8,000 Bosnians, mostly men and boys, were rounded up and systematically murdered.
Members of the Mothers of Srebrenica, an organization of survivors of Srebrenica and a nearby village, Zepa, were present at The Hague on Wednesday.
A banner placed outside the court building by a group of Bosnians — and removed before the proceedings began — said “Radovan Karadzic / Genocide — Adolf Hitler Holocaust.”
At the Potocari Memorial Center close to the scene of the Srebrenica massacre, local residents, including relatives of the victims, gathered to watch the tribunal’s result through an online video stream.
The appeals were little covered by the news media in Serbia, where The Hague’s tribunal is widely viewed as anti-Serb — a view likely to be reinforced by Wednesday’s ruling.
The appeals ruling is final. Mr. Karadzic will serve his sentence in one of the European countries that have agreed to take tribunal prisoners.
“The measure of success or failure of this verdict will not be in where Radovan Karadzic makes his residence between now and his death, or in what a gaggle of self-seeking politicians will do in the next week or month,” said Eric Gordy, professor at the School of Slavonic and East European Studies at University College London.
“What will matter about the verdicts will be the documentary record that they establish,” he said.
But the overriding question to Mr. Gordy, who has long followed the tribunal’s trials, is whether the records provide a ground for discussion and conciliation among people who have been taught “that they always need to think of themselves as victims and of the people around them as their enemies.”