The International Criminal Court (ICC) has found the Congolese warlord, Thomas Lubanga, guilty of recruiting and using child soldiers between 2002 and 2003.
It is the court’s first verdict since it was set up 10 years ago. He will be sentenced at a later hearing.
He headed a rebel group during an inter-ethnic conflict in a gold-rich region of Democratic Republic of Congo.
The prosecution accused him 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, Lubanga bore responsibility for the recruitment of child soldiers under the age of 15 who had participated actively on the frontline.
Lubanga, who was arrested in 2005, has the right to appeal against the guilty verdict on all three war crimes charges.
He could face a maximum sentence of life imprisonment. The court cannot impose the death penalty.
US-based Human Rights Watch says more than 60,000 people were killed in the conflict between Hema and Lendu ethnic groups in Ituri, in north-eastern DR Congo.
It took the presiding judge Adrian Fulford 30 minutes to deliver the verdict.
The evidence demonstrated that children endured harsh training regiments and were subjected to hard punishment,” AFP news agency quotes him as saying.
“The evidence demonstrated that the children were deployed… and took part in the fighting,” he said.
But the judge was also very critical of the prosecution’s initial investigation, saying the intermediaries it had used in Ituri had led to unreliable evidence.
This had cost the court time and expense, he said.
The BBC’s Anna Holligan in The Hague says the guilty verdict means victims and their families will now be entitled to reparations from the court.
Amnesty International said the conviction of the Congolese rebel leader showed the ICC could bring the world’s worst offenders to justice.
“It will help to strip away the impunity they 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, from the UK-based group said in a statement.
As well as being the ICC’s first verdict, the Lubanga case is also the first international trial focusing on the use of child soldiers.
Analysts say it could set legal precedents for others accused of similar crimes.
The ICC issued its first arrest warrant in 2005 against the Ugandan rebel leader, Joseph Kony, who remains at large.
His Lord’s Resistance Army is accused of committing atrocities in several central African countries.
Others ICC suspects include Saif al-Islam Gaddafi, the son of the former Libyan leader, and several members of the Sudanese government, including President Omar al-Bashir.