[1] He led a cavalry squadron in the Battle of Yarmuk, and Caliph Umar (r. 634–644) appointed him first as governor of Homs and later of Upper Mesopotamia.
[2] Caliph Umar is said to have been impressed by him, and to have opened the treasury (or the arsenal, according to other accounts) for him to take what he wished; Habib only took a set of weapons, leaving the treasure untouched.
The campaign was a great success for the Arabs: Habib's forces took Melitene and defeated the Byzantine governor of Armenia, Maurianos, in a night attack near Dvin.
According to the Armenian historian Sebeos, the Arabs pursued the defeated Byzantine commander as far as Caucasian Iberia or even the Black Sea, and took Trapezus and Theodosiopolis.
[3][2] Habib was briefly appointed governor of the subdued Armenian territories, but was then recalled to take command of the borderlands with Byzantium in northern Syria, centred on Qinnasrin, from where he was engaged in fighting against the Mardaites and the Byzantines.
[2][5][6] Historian Wilferd Madelung however considers stories of Uthman's requesting aid against fellow Muslims a later invention.
He played a major role during the first day, when Ibn Budayl advanced towards Mu'awiyah's position in the centre, with the aim of personally killing the Syrian leader.
One of Ali's generals, al-Ashtar, managed to rally the retreating right wing and rescue Ibn Budayl, but a new assault by the latter on Mu'awiyah's position failed and he was killed.
[8] According to Ibn Khallikan, Habib's "signal service at the Battle of Siffin" made him one of Mu'awiyah's favourite generals.