The Gulf state of Qatar has been mediating between various Darfur groups and the government in Khartoum with a view to finding a lasting peace in Sudan's western region.
The Sudan Liberation Army, a major faction led by Abdelwahid Nur, has so far refused to have any negotiations with the government.
Earlier this month it clashed with the army in the fertile Jebel Marra plateau in the heart of Darfur.
On Wednesday, Sudanese authorities re-arrested 15 members of Jem after releasing them following a truce with the group.
Adam Bakr, the lawyer representing the rebels, said they were arrested when they went to Al-Fashir, the capital of north Darfur.
Omar Alsaleh, Al Jazeera's correspondent at the ongoing talks in Doha, said: "There will be anger obviously by the signing of this agreement.
"Jem said that if there is a parallel agreement with other groups they will walk out.
"[But] diplomats said that Jem are under tremendous pressure to stay in Doha and stick to the peace talks."
The LJM and the Sudanese government will be signing the ceasefire agreement on two different papers, said our correspondent.
"The first one will be the framework agreement. This will lay out how the process will continue between the LJM and the government of Sudan," he said.
"The other important thing is that they'll be signing a ceasefire - a ceasefire for three months."
Scott Gration, the US envoy to Sudan, has urged all parties to the Darfur conflict to seize the "little window" for a peace agreement before presidential, parliamentary and state elections next month.
"If we can get a jump on a Darfur peace agreement, then we should, because there's going to be a lot of things keeping us from focusing on Darfur," Gration told reporters in Nairobi last week before he travelled to Doha.
"The framework agreement "has to be turned into a more formalised agreement ... If there is going to be a comprehensive and lasting peace in Darfur, all rebel groups need to be involved."
The conflict in Darfur has pitched ethnic African tribesmen against the Arab-dominated Khartoum government, claiming the lives of up to 300,000 lives - from the fighting as well as famine and disease - and displacing 2.7 million people, according to the UN.
Sudan, whose president Omar al-Bashir has been indicted by the International Criminal Court (ICC) over war crimes in Darfur, disputes the toll and says only 10,000 have died.