The ex-ruler, Habre, earlier denied the charges and refused to recognize the legitimacy of the court but left everyone in the court surprised when he showed no emotions after hearing the verdict with his face obscured partly by a turban and sunglasses.
According to Human Rights Watch, the decision makes Habre the first African former head of state to be convicted on the continent and it's also the first time that a court of one country has prosecuted the former ruler of another country over human rights crimes.
U.S. Secretary of State John Kerry welcomed Monday's verdict. "This ruling is a landmark in the global fight against impunity for atrocities, including war crimes and crimes against humanity," Kerry said in a statement released by CNN.
"As a country committed to the respect for human rights and the pursuit of justice, this is also an opportunity for the United States to reflect on, and learn from, our own connection with past events in Chad,"
Zeid Ra'ad Al Hussein, the U.N. high commissioner for human rights, descibed the ruling as groundbreaking.
"After years of struggle and many setbacks on the way to justice, this verdict is as historic as it was hard-won. I sincerely hope that today, at last, Habre's victims will experience some sense of relief. In a world scarred by a constant stream of atrocities, the ramifications of this verdict are global. "