Their convictions included recruiting child soldiers, attacks on peacekeepers and forced marriages.
“Today’s appeals judgment is a final condemnation of one of the most brutal and notorious rebel groups in modern times,” acting prosecutor Joseph Kamara said.
“With the end of this trial there is now a final recognition of their crimes, and there is a strong measure of justice and accountability for their victims,” he said in a statement.
The dismissal of the appeal leaves Charles Taylor, the former president of neighbouring Liberia, as the only remaining inductee of the Freetown-based court.
Taylor, whose trial is being held in The Hague for security reasons, is accused of stoking Sierra Leone’s conflict in exchange for diamonds from the east of the country.
The war was characterised by bands of rebels, including drug-addled child soldiers, killing, raping and mutilating civilians.
“During the Sierra Leone civil war it was more dangerous to be a civilian than a soldier,” Kamara said.