Nasr fought alongside his father in the Battle of al-Uqhuwana near Tiberias in 1029, where Salih was killed by a Fatimid army led by Anushtakin al-Dizbari.

Nasr was the eldest son of Salih ibn Mirdas,[1][2] the preeminent emir of the Bedouin (nomadic) Banu Kilab tribe and founder of the Mirdasid dynasty.

By 1025, Salih's Aleppo-based Mirdasid emirate covered much of northern Syria, the western Jazira (Upper Mesopotamia) and the central Syrian towns of Sidon, Baalbek and Homs.

In 1029, he supported his ally, Hassan ibn Mufarrij, the Jarrahid emir of the Bedouin Banu Tayy tribe, against a Fatimid army led by Anushtakin al-Dizbari.

[4] The youth and inexperience of Nasr and Thimal was viewed by the Byzantine katepano of Antioch, Michael Spondyles, as an opportunity to establish a protectorate over the Mirdasids' domains and prevent the re-establishment of Fatimid rule in the wake of Salih's death.

[4][5] In the aftermath, Spondyles was dismissed by Emperor Romanos III (r. 1028–1034), who resolved to avenge the Byzantine loss, install his ally, the former emir of Aleppo Mansur ibn Lu'lu', in place of the Mirdasids, and in the process, achieve a glorious military victory over the Arabs.

[6] Romanos III arrived at Antioch with a 20,000-strong army, composed mostly of mercenaries,[7] on 20 July 1030, and sent a messenger to Nasr and Thimal demanding they cede Aleppo to him.

[8] Nasr rejected the demand, detained the envoy and sent his own diplomatic mission, led by his cousin Muqallid ibn Kamil, to persuade Romanos to desist from attacking Aleppo.

[10] Nasr and Thimal, meanwhile, evacuated their families from the city, and mobilized the Kilab, the Banu Numayr and other Bedouin tribes, as well as local Muslims from Aleppo and its hinterland.

[12] Romanos, whose army was encamped in a barren plain during the summer heat, sent a force to survey the fortress of Azaz,[7] but these troops were all killed or captured by the Mirdasids.

[16] In the account of the 13th-century Aleppine historian Ibn al-Adim, Nasr and his men seized the citadel when Thimal was in the Kilabi tribal camps in Aleppo's outskirts attempting to persuade his estranged wife to return to the city.

[18] The modern historian Suhayl Zakkar asserts that Yahya's account was the more likely scenario, particularly because Nasr immediately appealed for Byzantine forgiveness and protection, offering an annual tribute of 500,000 dirhams, despite his decisive victory over Romanos at Azaz;[19] Zakkar holds Nasr's spontaneous offer to the Byzantines was prompted by Kilabi dissent or threats organized by Thimal in response to the latter's ouster.

[21] While Romanos adamantly sought to include Nasr's emirate in the proposed treaty, he died and was replaced in 1034 by Emperor Michael IV (r. 1034–1041); the latter was more conciliatory toward Fatimid concerns.

[23] According to Zakkar, "Byzantium, which by this Treaty, had solved most of its problems with the Fatimid Caliphate, lost interest in Aleppo, or at least no longer deemed it to be of the same political importance.

During Mirdasid rule, a large influx of peasants and nomads from the countryside moved to Aleppo, resulting in the establishment of crowded quarters and suburbs within and outside the city's walls.

[31] Nasr's vassalage to the Byzantines provoked the opposition of Salim ibn al-Mustafad, Aleppo's ra'is al-balad (municipal chief) and leader of the ahdath (urban paramilitaries), who had been appointed by Salih.

[30] Nasr's acquisition of Hims in 1037 came at the expense of its Fatimid-appointed, Berber governor, Ja'far ibn Kulayd al-Kutami, who was concurrently dismissed from the governorship.

The latter was already perturbed by the expansion of the Mirdasid realm to Hims, which would give the Byzantine-backed Mirdasid–Numayrid alliance full control of the lowland regions and routes between the Iraqi frontier and the Mediterranean Sea.

Anushtakin did not await Cairo's response, and he and Ibn Kulayd mobilized their forces to assert direct Fatimid rule over northern Syria.

[34] Upon hearing of Anushtakin's campaign against him, Nasr mobilized his local and Kilabi forces, including Thimal and his loyalists, and set out to confront the Fatimid coalition.