As the Iraqis gained the battlefield advantage, Amr proposed to Mu'awiya that their men tie leaves from the Qur'an at the tips of their lances in an appeal to Ali's men to settle the conflict peacefully. It served as a successful ruse which ended the fighting as the battle turned in Ali's favor and sowed uncertainty in Ali's ranks. The Caliph heeded the majority will in his army to settle the matter diplomatically; an arbitration was agreed with Amr representing Mu'awiya and Abu Musa al-Ash'ari representing Ali. Amr met with Ali once and the two exchanged insults, but Ali ultimately agreed to Amr's condition that he omit his caliphal title, amīr al-muʾminīn (commander of the faithful), from the preliminary arbitration document drafted on 2 August. The omission effectively placed Ali and Mu'awiya on an equal political footing and thereby weakened Ali's leadership position over the Muslim polity.
Amr and Abu Musa likely met twice, at Dumat al-Jandal and then Adhruh, to forge an agreement. At Dumat al-Jandal, Amr succeeded in gaining Abu Musa's recognition that Uthman was wrongfully killed, a verdict opposed by Ali and which strengthened Syrian support for Mu'awiya, who had taken up the cause of revenge for the death of his kinsman Uthman. At the last meeting in Adhruh, the office of the caliphate was discussed, but the meeting ended in violence and without agreement; during the brawl, Amr was physically assaulted by a Kufan partisan of Ali, but the latter was fended off by one of Amr's sons. Abu Musa retired to Mecca, while Amr and the Syrians returned to Mu'awiya and recognized him as amīr al-muʾminīn before formally pledging allegiance to him in April/May 658. As a result, Amr was among those invoked in a ritual curse issued by Ali during the morning prayers and became the subject of derision among the Kufan core of Ali's supporters.
Amr was permitted by the Caliph to retain personally the surplus revenues of the province after the payment of the troops' stipends and other government expenses. He increased the original garrison at Fustat, numbering some 15,000 soldiers, with the Syrian troops he brought with him. According to the historian Clive Foss "Amr ruled the country successfully, and with considerable independence and privilege, until his death". 2b1af7f3a8