The International Criminal Court (ICC) has found Congolese rebel leader Thomas Lubanga guilty of recruiting and using child soldiers between 2002 and 2003.
It is the Hague-based court's first verdict in its 10-year history.
Lubanga will be sentenced at a later hearing and could face a maximum of life imprisonment, though he has the right to appeal.
The 51-year-old warlord was arrested in Kinshasa in 2005 and his trial began in 2009. He was charged with recruiting and using child soldiers during the civil war in the Democratic Republic of the Congo (DR Congo), a conflict which ran from 1998-2003.
Prosecutors said Lubanga was the leader of the Union of Congolese Patriots (UPC) and its armed wing. He denied the claims and said he only was a political leader.
The panel of three judges ruled unanimously that evidence proved that as the leader of the UPC and its armed wing, Lubanga bore responsibility for the recruitment of child soldiers under the age of 15 who actively participated on the frontline.
"The evidence demonstrated that children endured harsh training regimens and were subjected to hard punishment," presiding judge Adrian Fulford said.
"The evidence demonstrated that the children were deployed and took part in the fighting."
Prosecutors said his role in the conflict was motivated by his will to retain control over Ituri province, a gold-rich region of DR Congro.
They also told the court that under his leadership the UPC's armed wing, the Patriotic Forces for the Liberation of Congo, abducted children as young as nine.
The children were taken to training camps, where they were repeatedly beaten and drugged, while the girls were also used as sex slaves.
Amnesty International welcomed the conviction.
"It will help to strip away the impunity [war criminals] have enjoyed for crimes under international law because national authorities have consistently failed to investigate these crimes. This guilty verdict demonstrates that the ICC can step in to bring them to justice," Michael Bochenek, legal and policy director of the UK-based group, said.
Lubanga was one of 20 suspects who have been the subject of ICC arrest warrants. The court issued its first warrant in 2005 against the Ugandan rebel leader Joseph Kony, of the Lord's Resistance Army
Other ICC suspects include Saif al-Islam Gaddafi, son of the late Libyan leader Muammar Gaddafi, and several members of the Sudanese government, including president Omar al-Bashir.