Last year, appeals judges at the court overturned a war-crimes conviction for Jean-Pierre Bemba, a former vice president of the Democratic Republic of Congo. And this year, a former president of Ivory Coast, Laurent Gbagbo, and one of his aides, were acquitted of crimes against humanity.

Burundi and the Philippines, outraged over Ms. Bensouda’s investigations of their leaders, have quit the court. And the United States, which is not a member of the court, revoked Ms. Bensouda’s visa a few months ago over her effort to investigate allegations of war crimes committed in Afghanistan — including any that may have been perpetrated by American forces.

“The past few months, and even last year, have been filled with disappointments and setbacks for the I.C.C.,” said Amal Nassar, The Hague representative for the International Federation for Human Rights, a Paris-based advocacy group.

Still, Ms. Nassar expressed hope that the guilty verdict in Mr. Ntaganda’s case, should it stand up on appeal, “somehow restores hope and confidence in the court.”

Known for his pencil mustache and luxury lifestyle, Mr. Ntaganda was the chief of military operations for the Union of Congolese Patriots, a rebel group, and its armed faction, the Patriotic Forces for the Liberation of Congo, in a conflict over control of land, trading routes and gold mines. Civilians were caught in the middle.

Mr. Ntaganda was first indicted in 2006 but only stood trial years later, after turning himself in at the United States Embassy in Kigali, the Rwandan capital, in March 2013. Experts suspect that he surrendered because he feared for his life: There had been a split in the latest rebel group he had formed, M23, and it appeared that he had lost the support of his Rwandan backers.

During the trial, Mr. Ntaganda told the court that he was “not a criminal” but a “trained officer” who always protected civilians.