As the senior member of the Hamdanid dynasty, he inherited the family power base around Mosul from his father, and was able to secure it against challenges by his uncles. Hasan became involved in the court intrigues of the Abbasid Caliphate in Baghdad, and, between 942 and 943, he, with the assistance of his brother Ali (known as Sayf al-Dawla), established himself as amir al-umara, or de facto regent for the Abbasid caliph. He was driven back to Mosul by Turkish troops, however, and subsequent attempts to challenge the Buyids who seized control of Baghdad and lower Iraq ended in repeated failure. Twice, his capital Mosul was captured by Buyid forces, which were, however, unable to defeat local opposition to their rule. As a result of his failures to retain power, Nasir al-Dawla declined in influence and prestige. He was eclipsed by the actions of his brother Ali, who established his rule more firmly over Aleppo and northern Syria. After 964, Nasir al-Dawla's eldest son Abu Taghlib exercised de facto rule over his domains, and in 967, Abu Taghlib and his brothers deposed and imprisoned their father, who died in captivity a year or two later.
Nasir al-Dawla was born al-Hasan ibn Abdallah, the eldest son of Abu'l-Hayja Abdallah ibn Hamdan (died 929), son of Hamdan ibn Hamdun ibn al-Harith, who gave his name to the Hamdanid dynasty. The Hamdanids were a branch of the Banu Taghlib, an Arab tribe resident in the area of the Jazira (Upper Mesopotamia) since pre-Islamic times. The Taghlibs had traditionally controlled Mosul and its region until the late 9th century, when the Abbasid government tried to impose firmer control over the province. Hamdan ibn Hamdun was one of the most determined Taghlibi leaders in opposing this move. Notably, in his effort to fend off the Abbasids, he secured the alliance of the Kurds living in the mountains north of Mosul, a fact which would be of considerable importance in his family's later fortunes. Family members intermarried with Kurds, who were also prominent in the Hamdanid military.
Hamdan's possessions were captured in 895 by the Abbasid Caliph al-Mu'tadid, and Hamdan himself was forced to surrender near Mosul after a long chase. He was put in prison, but his son Husayn ibn Hamdan, who had surrendered the fortress of Ardumusht to the Caliph's forces, managed to secure the family's future. He raised troops among the Taghlib in exchange for tax remissions, and established a commanding influence in the Jazira by acting as a mediator between the Abbasid authorities and the Arab and Kurdish population. It was this strong local base which allowed the family to survive its often strained relationship with the central Abbasid government in Baghdad during the early 10th century. Husayn was a successful general, distinguishing himself against the Kharijites and the Tulunids, but was disgraced after supporting the failed usurpation of Ibn al-Mu'tazz in 908. His younger brother Ibrahim was governor of Diyar Rabi'a (the province around Nasibin) in 919 and after his death in the next year he was succeeded by another brother, Dawud. Hasan's father Abdallah served as emir (governor) of Mosul in 905/6–913/4, was repeatedly disgraced and rehabilitated as the political situation changed in Baghad, until re-assuming control of Mosul in 925/6. Enjoying firm relations with the powerful commander of the caliphal army, Mu'nis al-Khadim, in 929 he played a leading role in the short-lived usurpation of Al-Qahir (who would later reign as caliph in 932–934) against Al-Muqtadir (r. 908–932), and was killed during its suppression. According to the researcher Marius Canard, Abdallah established himself as the most prominent member of the first generation of the Hamdanid dynasty, and was essentially the founder of the Hamdanid Emirate of Mosul.
During his absence in Baghdad in his final years from 920/921 on, Abdallah relegated authority over Mosul to Hasan. After Abdallah's death, however, al-Muqtadir took the opportunity to avenge himself upon the Hamdanids, and appointed an unrelated governor over Mosul, while Abdallah's domains were divided among his surviving brothers. Faced with the claims of his uncles, Hasan was left in charge of a small portion, on the left bank of the Tigris. In 930, after the caliph's governor died, Hasan managed to regain control over Mosul, but his uncles Nasr and Sa'id soon removed him from power and confined him to the western parts of the Diyar Rabi'a. In 934, Hasan again recovered Mosul, but Sa'id, residing in Baghdad and supported by the caliphal government, evicted him again. Hasan fled to Armenia, from where he orchestrated Sa'id's murder. Only then did his troops occupy Mosul and establish him permanently as its ruler. Finally, after defeating caliphal forces under the wazir Ibn Muqla and the Banu Habib, his rivals among the Taghlib, in late 935 the Caliph al-Radi was forced to formally recognize him as governor of Mosul and the entire Jazira, in exchange for an annual tribute of 70,000 gold dinars and supplies of flour for the two caliphal capitals of Baghdad and Samarra.
Resistance to Hasan's rule outside of his family's core region around Mosul remained, however—in Diyar Bakr, the governor of Mayyafariqin, Ali ibn Ja'far, rebelled against Hasan, and in Diyar Mudar, the Qaysi tribes of the region around Saruj also revolted. Hasan subdued them and secured control over the entire Jazira by the end of 936, due to the efforts of his brother Ali, who was given the governorship of the two provinces as a reward. In the meantime, the defeated Banu Habib, some 10,000 strong and under the leadership of al-Ala ibn al-Mu'ammar, left their lands and fled to territory controlled by the Byzantine Empire. This unprecedented move may be explained by the fact that a significant portion of the tribe still practised Christianity, or by pressure upon their grazing lands by tribes from the south, but the primary goal of the move was to escape from Hamdanid authority and taxation. Hasan also attempted to extend his control to Sajid-ruled Azerbaijan in 934 and 938, but his efforts failed.