Hissène Habré has been sentenced to life in prison, with campaigners saying "today will be carved into history"
The former president of Chad has been found guilty of crimes against humanity at a special court in Senegal.
Hissène Habré was sentenced to life in prison following the ruling at the Extraordinary African Chambers.
He was also found guilty of summary execution, torture and rape, The Guardian reports.
Habré ruled Chad between 1982 and 1990. The New York Times says international groups had been campaigning to have the former ruler held accountable for tens of thousands of deaths in the country.
The trial is the first in the world in which the courts of one country prosecuted the former ruler of another for alleged human rights crimes, according to campaigners with Humans Rights Watch.
Reed Brody of Human Rights Watch said: "Over 25 years ago, Souleymane Guengueng, a deeply religious civil servant who watched dozens of his cellmates succumb to torture and disease in Hissène Habré’s Chadian prisons, took an oath that if he ever got out of jail alive, he would bring his tormentors to justice.
"Today I sat alongside Souleymane and other survivors as Habré was convicted of atrocities by a special court in Senegal, where he’s lived in luxurious exile since his overthrow in 1990".
Mr Brody added that today "will be carved into history as the day that a band of unrelenting survivors brought their despot to justice".
Habré - who has been dubbed 'Africa's Pinochet' by some critics - has two weeks to appeal following today's verdict.