The Doha meeting would be a prelude to agreeing on a new constitution and then holding elections in the African nation that was thrown into turmoil last April.
Chad's military government and dozens of opposition groups have started peace talks in Qatar as a first step towards ending a rebellion and holding elections.
Chad's Prime Minister Albert Pahimi Padacke and African Union Commission head Moussa Faki Mahamat told the opening of the conference on Sunday that both sides would have to make "concessions" for the talks to succeed.
But the process risks being protracted and complicated.
The landlocked African nation was thrown into turmoil by the killing of longtime leader Idriss Deby Itno in battle with rebels in the country's north last April.
His son, Mahamat Idriss Deby Itno, took over the country after his death, fronting a 15-member military junta and vowing to hold free elections.
Some 44 armed rebel and opposition groups were invited to the Doha meeting - though some were missing at the opening, which had already been delayed from February 27.
Diplomats said these "precursor" talks could take weeks and that a planned "national dialogue" due to start on May 10 may have to be delayed.
Elections under new constitution
Under the younger Deby's plan, the dialogue would be a prelude to agreeing on a new constitution and then holding elections.
Chad has a long history of volatility since gaining independence from France in 1960 and tens of thousands have died in various conflicts.
It has a large and shifting constellation of armed opposition groups.
As a condition for the Doha talks, Chadian rebels called for a general amnesty and the release of "prisoners of war" and the return of confiscated assets.
The military government says it has released hundreds of prisoners and amnestied several prominent leaders.
However, it has so far excluded the Front for Change and Concord in Chad (FACT) - the Libya-based group that launched the offensive in which Idriss Deby Itno was killed.