Nouri worked as a postal officer before joining the FROLINAT rebel group in 1969 formed of Muslims from northern and central part of the country opposing the regime of François Tombalbaye. When the group divided in 1976, he sided with Hissène Habré. After the 1978 Khartoum Accord, Nouri became Minister of the Interior of the Government of Chadian National Unity (GUNT). As Habré’s associate he held many other ministerial positions throughout his career.
Following Habré’s downfall in 1990, Nouri passed his allegiance to Habré’s successor, Idriss Déby, under whom he rose once again to a prominence. He served as a member of the government from 1995 to 2004. Afterwards, he was sent as Chad’s ambassador to Saudi Arabia. At this period, he broke with Déby in 2006 and joined armed opposition against him.
Nouri helped to unify opposition and became a leader of the most powerful Chadian rebel group, the Union of Forces for Democracy and Development (UFDD). He initiated a series of attacks against government positions in eastern Chad in autumn 2006, posing a serious challenge to Déby. After the failure of a series of talks held in Libya in 2007, Nouri coordinated with two other rebel groups and launched a direct attack on the Chadian capital in February 2008. He was repelled after days of heavy fighting by the army with the backing of French troops.
Two years later, Nouri and two other rebel chiefs were expelled from Sudan, where they had based their operations for many years, after Sudan and Chad normalised relations.
Nouri’s UFDD has meanwhile established bases in southern Libya on the northern border with Chad. Mahamat Nouri was expelled from Libya to Qatar in 2010 before arriving in France a year later.
Charges against Nouri were filed in May 2013 in Chad.
On 18 January 2017, the French authorities imposed for six months freeze on Nouri’s financial assets.
In May 2017, on the basis of the report from the French Office for Protection and Refugees and Stateless Persons (OFPRA), an investigation into crimes in which he was allegedly implicated between 2005 and 2010 in Chad and Sudan were opened and assigned to the Central Office for Combatting Crimes Against Humanity, Genocide and War Crimes.
On 3 January 2019, the prosecutor from Tripoli, Libya, issued an international warrant of arrest against Nouri and 23 other Chadians.
On 17 June 2019, Nouri was arrested by the French police, as well as two other persons on suspicion of crimes against humanity. Mahamat Nouri was interviewed on 21 June by the examining magistrates who decided to charge him with crimes against humanity and participation in a criminal organization in order to prepare crimes against humanity. Nouri is suspected of having ordered recruitments of fighters, including minors between 2005 and 2010 in Chad and Sudan.
Mahamat Nouri was placed in pre-trial detention.
On 27 March 2020, Mahamat Nouri was released from detention on sanitary grounds, due to the covid-19 pandemic. He benefited from a health precautionary measure due to his age (he was 73 years old at the time of the decision). The judge ordered his judicial supervision.