He was reported dead on Tuesday, Aged 68, a day after he won re-election for a sixth term in office.
His death was confirmed by Chadian national army after gunshot injuries in a fight with rebels.
There has been a prolonged battle in the African country between government forces and the rebel Front for Change and Concord in Chad (FACT).
The unrest had escalated in recent days as anti-government fighters approached N’Djamena, the capital city.
The president was commanding his army in the battle against rebel forces in the far north over the weekend.
Azem Agouna, a spokesman of the Chadian army, said in a broadcast that the late leader breathed his last defending the sovereign nation on the battlefield.
Meanwhile, Déby was one of the longest-serving presidents of Chad, having stayed in office for about 30 years.
He came to power in a rebellion in 1990 and won a sixth term on Monday in a controversial poll boycotted by the opposition.
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