Chadian President Idriss Deby Itno greets a crowd of journalists and supporters as he arrives to casts his ballot at a polling station in N djamena, on April 11, 2021. AFP
After a mass trial, they were sentenced for "acts of terrorism, mercenarism, recruitment of child soldiers and assaulting the head of state," said Mahamat El-Hadj Abba Nana, prosecutor for the capital N'Djamena.
He did not give a detailed figure for those jailed, saying only that "more than 400 were sentenced" to life, while 24 other defendants were acquitted.
The trial opened last month behind closed doors at Klessoum prison, 20 kilometers (12 miles) southeast of the capital.
In early 2021, the country's main rebel group, the Front for Change and Concord in Chad (FACT), launched an offensive on the north of the country from bases in Libya.
On April 20, the army announced that Marshal Deby, Chad's iron-fisted ruler for the previous three decades, had died from wounds sustained in the fighting.
His death was announced just a day after he had been declared the victor of a presidential election that gave him a sixth term in office.
He was immediately succeeded by one of his sons, General Mahamat Idriss Deby Itno, who took the helm at the head of a 15-member military junta.
Several defendants were also ordered to pay damages of more than $32 million to the state and $1.6 million to the ex-president's family, said FACT lawyer Francis Lokoulde, who suggested there would be an appeal.
"It's a masquerade that follows no law, no convention", said FACT leader Mahamat Mahdi Ali.
"All that comes from a willingness to criminalize our struggle. The verdict is a non-event," he said.
Defense lawyers had protested at the very short notice after the mass trial had been announced just days before it started on February 13.
Mahamat Idriss Deby Itno had promised to hold free elections within 18 months, but that deadline was extended for another two years.
Protests last October to mark the initially promised end to military rule met with a deadly crackdown.
The Chadian authorities first put the death toll in the capital at around 50, before updating that figure to 73 deaths. Opposition groups say the number is higher.
The Geneva-based World Organization against Torture (OMCT) accused the Chadian authorities of summary executions and torture.
A total of 262 people were then handed terms of between two and three years after a trial in the notorious Koro Toro prison, isolated in the desert 600 kilometers from N'Djamena.
The remote location and proceedings drew condemnation from international human rights groups.
Human Rights Watch not only denounced the mass trial but also the murders, forced disappearances, and torture that preceded it.
The main leaders of Chad's opposition now live in hiding or in exile, even though the junta lifted a suspension of several opposition parties in January.
Despite criticism of his authoritarian rule, the elder Deby was a key ally in the West's anti-jihadist campaign in the unstable Sahel, particularly due to the relative strength of Chad's military.