After a mass trial, the accused 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.
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 Front for Change and Concord (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.
The trial opened last month behind closed doors at Klessoum prison, 20 kilometers southeast of the capital.
Human Rights Watch not only denounced the mass trial but also the murders, forced disappearances and torture that preceded it.
Defense lawyers had protested at the very short notice after the mass trial had been announced just days before it started on February 13.
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 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.