On Saturday, Colonel Adoum Yacoub, a spokesman for 19 groups that had pulled out, told AFP their concerns had been addressed.
"We had discussions with the mediator with whom we shared our grievances in writing and we received all the answers," he said.
Brahim Hissein, a spokesman for Chad's main armed opposition movement, the Front for Change and Concord in Chad (FACT), said they had spoken to the mediator on Thursday and decided to "give the talks a new chance."
Around 50 groups have been negotiating for more than four months in Doha, with the aim of holding an inclusive national dialogue to pave the way for elections.
But a host of them withdrew from the talks on July 16, accusing the government of seeking to destabilize peace efforts.
On Thursday, the Qatari mediator handed a draft peace agreement to the rebel groups and the Chadian government.
Mahamat Mahdi Ali, the leader of FACT, told AFP: "There are two or three points to discuss... but it's a good start."
Government spokesman Abderaman Koulamallah praised "the foresight of (his) brothers".
The rebel groups who withdrew on July 16 did so less than 24 hours after Deby's administration announced that a national peace dialogue ahead of elections would start on August 20.
The rebels said the new date had been set without any consultation, describing it as an attempt to "exclude" many of the armed groups and their political allies from the dialogue.