[5][6] His father, Abd al-Aziz ibn Marwan, belonged to the wealthy Umayyad clan resident in the city, while his mother, Layla bint Asim, was a granddaughter of the second Rashidun caliph Umar (r. 634–644).

Umar's grandfather, Marwan I (r. 684–685), was ultimately recognized by these tribes as caliph and, with their support, reasserted Umayyad rule in Syria.

[6] He often led the annual Hajj pilgrimage in Mecca and showed favor toward the Islamic legal scholars of Medina, notably Sa'id ibn al-Musayyab.

[6] Under Umar's generally lenient rule, the Hejaz became a refuge for Iraqi political and religious exiles fleeing the persecutions of al-Hajjaj ibn Yusuf, al-Walid's powerful viceroy over the eastern half of the Caliphate.

[6] Despite his dismissal, Umar remained in al-Walid's favor, being the brother of the caliph's first wife, Umm al-Banin bint Abd al-Aziz.

[12] Alongside Raja ibn Haywa, an influential religious figure in the Umayyads' court, Umar served as a principal adviser of Sulayman.

[6] Likewise, he was at the caliph's side at the Muslims' marshaling camp at Dabiq in northern Syria, where Sulayman directed the massive war effort to conquer the Byzantine capital of Constantinople in 717.

[6] The elevation of Umar, a member of a cadet branch of the dynasty, in preference to the numerous descendants of Abd al-Malik surprised these princes.

This was mainly relevant to the non-Arab troops in the Muslim army, who had not been entitled to the same shares in spoils, lands and salaries given to Arab soldiers.

[23]Possibly to stave off potential blowback from opponents of the equalization measures, Umar expanded the Islamization drive that had been steadily strengthening under his Marwanid predecessors.

[24] According to Khalid Yahya Blankinship, he put a stop to the ritual cursing of Caliph Ali (r. 656–661), the cousin and son-in-law of Muhammad, in Friday prayer sermons.

[24] Umar is credited with having ordered the first official collection of hadith (sayings and actions attributed to the Islamic prophet Muhammad), fearing that some of it might be lost.

[25] He subdivided the vast governorship established over Iraq and the eastern Caliphate under Abd al-Malik's viceroy al-Hajjaj ibn Yusuf.

[14] Sulayman's appointee to this super-province, Yazid ibn al-Muhallab, was dismissed and imprisoned by Umar for failing to forward the spoils from his earlier conquest of Tabaristan along the southern Caspian coast to the caliphal treasury.

Although many of these appointees were pupils of al-Hajjaj or affiliated with the Qays faction, Umar chose them based on their reliability and integrity, rather than opposition to Sulayman's government.

[27] After his accession in late 717, Umar ordered the withdrawal of the Muslim army led by his cousin Maslama ibn Abd al-Malik from their abortive siege against Constantinople to the regions of Antioch and Malatya, closer to the Syrian frontier.

[6] In 718, he successively deployed Iraqi and Syrian troops to suppress the Kharijite rebellion of Shawdhab al-Yashkuri in Iraq, though some sources say the revolt was settled diplomatically.

[30] He proposed it was the massive losses faced by the Arabs in their abortive siege against Constantinople, including the destruction of their navy, that caused Umar to view his positions in al-Andalus, separated by the rest of the Caliphate by sea, and Cilicia as acutely vulnerable to Byzantine attack.

[30] Although he halted further eastward expansion, the establishment of Islam in a number of cities in Transoxiana precluded Umar's withdrawal of Arab troops from there.

[21] In the assessment of H. A. R. Gibb, Umar acted to prevent the collapse of the caliphate by "maintaining the unity of the Arabs; removing the grievances of the mawālī; and reconciling political life with the claims of religion.