South Sudan President Salva Kiir and the rebels both accepted the plan offered by international mediators on Saturday and said their forces would halt the fighting within a few days.
Kiir and the rebel forces led by his former vice president began an all-out conflict last month. Kiir's forces Saturday announced they had driven the rebels out of the provincial capital of Bor.
Negotiating teams from both sides were already in Addis Ababa, the capital of neighboring Ethiopia, on Saturday and both pledged they would sign the cease-fire pact.
A representative of the rebels told the Sudan Tribune that the cease-fire plan met its conditions, which included allowing humanitarian aide into the contested areas and the withdrawal of foreign troops that had been assisting Kiir's army.