The talks, which should have begun in February, have been marred by delays as Chad's myriad rebel groups, meeting in Qatar, squabbled over whether to attend.
Crucial national talks on the future of Chad that the ruling junta says will pave the way for elections are set to begin on Saturday but the forum has been overshadowed by delays and boycotts.
More than 1,400 delegates from the military government, civil society, opposition parties, trade unions and rebel groups will gather in capital N'Djamena for the "national dialogue" that is scheduled to last three weeks.
The talks are the brainchild of junta chief General Mahamat Idriss Deby who took power in April 2021 at the age of just 37 after his father, who ruled for 30 years, was killed during a military operation against rebels.
He has said the forum should open the way to "free and democratic" elections after an 18-month rule by the junta – a deadline that France, the African Union (AU) and others have urged him to uphold.
The UN chief said on Friday that Chad's upcoming landmark talks offer a "historic opportunity" for the African nation to return to stability and set a course towards democracy.
UN Secretary-General Antonio Guterres offered congratulations to Chad's transitional authorities and the country's people and acknowledged "the efforts made by all other stakeholders to reach this historic moment."
The UN chief also encouraged the participation of "all segments" of Chadian society, including women and young people, in the dialogue, and urged the political and military groups that have not yet signed the Doha peace agreement to join the peace process.
Challenges to the process
The "dialogue", which should have begun in February, has been marred by delays as Chad's myriad rebel groups, meeting in Qatar, squabbled over whether to attend. In the end, around 40 groups on August 8 signed up to a deal entailing a ceasefire and guarantee of safe passage.
On the agenda is lasting peace, reforming state institutions and a new constitution that will be put to a referendum.
Junta chief Deby signed a decree on Wednesday saying the decisions taken at the forum will be "legally binding".
Deby will speak at around 10:00 am (0900 GMT), said Saleh Kebzabo, a vice president of the forum's organising committee and one-time opponent of the elder Deby. The dialogue would then begin on Sunday or Monday, Kebzabo said.
The talks face major challenges according to observers: time pressure and the fact that two of the biggest rebel groups are not taking part.
They include the Front for Change and Concord in Chad (FACT), which triggered the offensive in the northeast last year that ended in the elder Deby's death.
Chad, one of the world's poorest countries, has endured repeated uprisings and unrest since its independence in 1960.