Ali Muhammad Ali Abd-Al-Rahman, a feared Sudanese militia leader, was found guilty of war crimes and crimes against humanity by the International Criminal Court on Monday, more than 20 years after he helped lead a brutal campaign of killing and destruction in Darfur.

Mr. Rahman, who is also known as Ali Kushayb, was one in a group of men accused by the court of carrying out a scorched-earth campaign that killed entire villages, including women and children, when the Sudanese government in Khartoum allied with local militias to stamp out a 2003 rebellion in Darfur.

Mr. Rahman was the first person to be tried at The Hague for atrocities in Darfur. Fearing for his life in Sudan, he surrendered to the court in 2020, but then denied all charges and claimed he was a victim of mistaken identity.

Joanna Korner, the presiding judge, said there was no doubt about who he was. Announcing the verdict, she described Mr. Rahman as a senior commander of the Janjaweed, the ruthless ethnic militia that did the army’s bidding in Darfur during that period, and became notorious for its raids and aerial bombings.

Citing harrowing accounts of mass killings and sexual violence carried out by Mr. Rahman’s forces, she said that not only did he give orders, but he was “personally involved” in beatings and gave direct orders for executions.

Human rights groups welcomed the verdict as a long-overdue step toward accountability for a period of dire abuses. It “should serve as a significant milestone in the pursuit of justice for crimes committed in Darfur more than two decades ago,” Tigere Chagutah, regional director of Amnesty International for eastern and southern Africa, said in a statement.