Chad's long-ruling President Idriss Deby Itno was re-elected to a sixth term with 79.32 percent of the votes cast in 11 April's election, according to provisional results from the electoral commission on Monday.
The cause of death was not yet clear.
Deby, 68, "has just breathed his last defending the sovereign nation on the battlefield" over the weekend, army spokesman General Azem Bermandoa Agouna said in a statement read out on state television.
Chad's President Idriss Deby Itno (centre) holds hands with his son Mahamat Idriss Deby Itno (right) in N'Djamena on 13 May 13 2013.
"A call to dialogue and peace is launched to all Chadians in the country and overseas in order to continue to build Chad together", said Agouna.
The army said a military council led by the late president's 37-year-old son Mahamat Idriss Deby Itno, a four-star general, would replace him.
"Two days ago news had come out from the USA embassy that they were evacuating personnel because there were rebels marching on the capital, and frankly the thought was '(Deby) will defeat them', because he has systematically defeated every attempted coup before now".
Deby's death comes just one day after he was declared the victor of a sixth term in office, marking over 30 years in power. Deby appears on course to extend his mandate despite mounting discontent over his management of oil wealth, questions over the fairness of the polls and concerns about a crackdown on dissent.
In February 2008, a rebel assault reached the gates of the presidential palace before being pushed back with French backing.
Deby seized power in an armed rebellion in 1990.
Former colonial power France keeps troops in Chad and heads a multinational force based in N'Djamena since 2014 to combat militants across the Sahel region.
Some residents of the capital, though, said they feared there was more to the story of Deby's demise. "His death disrupt things", a senior regional diplomat told Reuters.
The following year Chad launches a ground offensive in neighbouring Nigeria against the radical Islamist group Boko Haram, which is destabilising the countries bordering Lake Chad.
"We still don't have the whole story", Laith Alkhouri, a global intelligence adviser, told The Associated Press.