Thomas Lubanga, the Congolese warlord, has been found guilty of recruiting and using child soldiers between 2002 and 2003 by the International Criminal Court (ICC).
It is the court’s first verdict since it was set up 10 years ago.
Thomas Lubanga will be sentenced at a later hearing.
The warlord headed a rebel group during an inter-ethnic conflict in a gold-rich region of Democratic Republic of Congo.
The prosecution accused Thomas Lubanga of using children as young as nine as bodyguards, sex slaves and fighters.
In a unanimous decision, the three judges said evidence proved that as head of the Union of Congolese Patriots (UPC) and its armed wing, Thomas Lubanga bore responsibility for the recruitment of child soldiers who had participated actively on the frontline.
Thomas Lubanga, who was arrested in 2005, could face a maximum sentence of life imprisonment. The court cannot impose the death penalty.