On Monday, his campaign said he was headed to the northern part of the country to join troops in fighting "terrorists." Rebels based in Libya had attacked a border post on Monday, and advanced hundreds of kilometers south across the desert, towards the capital N'Djamena. Following the clashes, Chad's army said it had killed 300 rebels and quashed the offensive.
Transition council to take over
Army spokesman Azem Bermendao Agouna announced Deby's death on state television and radio, surrounded by military officers he referred to as the National Council of Transition.
An 18-month council will be led by Deby's 37-year-old son, Mahamat Idriss Deby Itno, the military said. A nightly curfew of will also be imposed during that time. The military said the country will hold "free and democratic elections" after that 18-month period.
"A call to dialogue and peace is launched to all Chadians in the country and abroad in order to continue to build Chad together," said Agouna. "The National Council of Transition reassures the Chadian people that all measures have been taken to guarantee peace, security and the republican order."
"In the face of this worrying situation, the people of Chad must show their attachment to peace, to stability, and to national cohesion,'' he said.
The general said that Deby had been taken to the capital after being wounded in battle.
Questions over the cause of death
The circumstances of Deby's death could not immediately be independently confirmed due to the remote location of the battlefield. However, some foreign observers have questioned how a head of state could have been killed, saying the death casts doubt on his protective guard.
Deby, 68, began his 30-year rule of the country in 1990, and is one of Africa's longest-serving leaders.
Last August, the National Assembly named Deby the first field marshal in Chad's history, after he led an offensive against jihadists in the west of the country.
France's 'brave friend' lost in terror war
France on Tuesday reacted to Deby's death saying it had lost a "brave friend" and Chad "a great soldier."
With experts fearing Deby's death could mean tremendous uncertainty for Chad going forward, the French presidency praised the former president and affirmed its support for Chad's stability and territorial integrity.
In a statement, Paris noted the formation of the interim council but said it hoped there would be a quick and peaceful return to civilian rule.
Both France and the United States are hoping their counter-terrorism efforts will not be pushed off course as Western countries depended heavily on Deby in the fight against Islamist militants such as Boko Haram in the Lake Chad Basin and groups linked to al-Qaeda and Islamic State in the Sahel.