After 30 years in power, Idriss Deby Itno was killed on the front line in a battle against rebels on Monday, just after securing his re-election as president.
The group the government is fighting is called the Front for Change and Concord in Chad, or Fact.
Now, Fact has vowed to take over the capital N'Djamena, after Deby's son, Mahamat Idriss Deby Itno, was named head of the transitional government.
Who are Fact and what do they want?
Fact is a political and military force founded by former politician and Deby critic SG Mahamat Mahdi Ali in March 2016, with the aim of overthrowing the government and seizing power in Chad.
The group is a splinter of the larger armed opposition Union of Forces for Democracy and Development.
Fact accused Deby of presiding over a repressive regime.
Swiss-based armed violence monitoring group Small Arms Survey says Fact is made up of "several hundred men", mostly of Daza ethnicity.
It has strongholds in northern Chad and southern Libya, mostly in the Tibesti Mountains.
The group has been based in Libya and had ties to a western Misratan militia. It made a non-aggression pact with the eastern-based Libyan National Army in 2017, following clashes.
Fact was, at least for some time, more involved in the Libyan conflict – where it appeared to operate as a mercenary force – than as a rebel group fighting the Chad government.
A 2017 report by the UN Panel of Experts on Libya said that Fact was unable to operate on the Chad side of the border.
Calling for Deby's resignation, Fact attacked a military post on the April 11 election day, leading to an armed confrontation with the Chadian army and a swift march towards the capital.
But the military claimed to have checked the rebel advance, saying that on Saturday a rebel column from Libya was “totally decimated”.
It is not possible to verify the claims and the military has not said if these clashes were where Deby was killed.
However, the Fact leader told Radio-France Internationale that the group was making a "strategic retreat".
Before the death of the president was announced, the US and British embassies said they were pulling staff out of the country due to clashes approaching the capital.
Fact criticised the formation of a military council by interim leader Mahamat Idriss Deby Itno, son of the dead president.
"We do not recognise any legitimacy in the military and family council. Idriss Deby is deceased, his son replaces him. It is not a dynasty, Chad is a secular republic. The institutional order must be restored," Mahdi Ali told Radio-France Internationale.
Insecurity in Chad
The central African nation has had a long history of rebellions during the 30-year reign of Deby – who himself came to power in a 1990 coup.
In 2008, clashes reached the gate of the presidential palace before Chad's army repelled rebel forces and pursued them east towards the Sudanese border.
Chad, a former French colony, is home to France's military Operation Barkhane, which deploys troops across the continent to fight extremism.
The Chadian military has played a major role in that effort, contributing troops to the UN peacekeeping mission in Mali.
Chadian soldiers also have long battled extremists from the Boko Haram group, which started in north-east Nigeria and spread to neighbouring countries.
In 2019, French armed forces intervened in northern Chad and launched air strikes at an armed group coming in from Libya.
Some 330,000 Chadians have been internally displaced by the clashes, the majority in the volatile Lake Chad region where Boko Haram fighters are most active.