Caliph Uthman (), who belonged to the Umayyad clan, appointed Abu al-A'war as governor of Jund al-Urdunn (military district of Jordan) with its capital in Tiberias. During the First Muslim Civil War, which followed the assassination of Uthman, Abu al-A'war served as one of Mu'awiya's generals in the battles against Caliph Ali (). He commanded a Sulaymi contingent at the Battle of Siffin in 657. Following the fighting at Siffin, Abu al-A'war was one Mu'awiya's representatives in the settlement negotiations with Ali, and he prepared the preliminary draft for the caliphal succession conference in Adhruh, a town in the Sharat highlands. In 658/59, Mu'awiya confirmed Abu al-A'war in his post in Jordan.