His father, Isaac ben Ezra, was a wealthy and learned Jew of Jaen. Hasdai acquired in his youth a thorough knowledge of Hebrew, Arabic, and Latin, the last-named language being at that time known only to the higher clergy of Spain. He also studied medicine, and is said to have discovered a universal panacea, called Al-Faruk. Appointed physician to the caliph Abd ar-Rahman III. (912-961), he, by his engaging manners, knowledge, character, and extraordinary ability, gained his master's confidence to such a degree that he became the caliph's confidant and faithful counselor. Without bearing the title of vizier he was in reality minister of foreign affairs; he had also control of the customs and ship-dues in the port of Córdoba. Hasdai arranged the alliances formed by the caliph with foreign powers, and he received the envoys sent by the latter to Córdoba. In 949 an embassy was sent by Constantine VII. to form a diplomatic league between the hard-pressed Byzantine empire and the powerful ruler of Spain. Among the presents brought by the embassy was a magnificent codex of Dioscorides' work on botany, which the Arabic physicians and naturalists valued highly. Hasdai, with the aid of a learned Greek monk named Nicholas, translated it into Arabic, making it thereby the common property of the Arabs and of medieval Europe.
Hasdai secured a great diplomatic triumph during the difficulties which arose between the kingdoms of Leon and Navarre, when the ambitious Queen Toda sought the aid of 'Abd al-Rahman in reinstating her deposed grandson Sancho. Hasdai was sent to the court of Navarre; and he succeeded after a long struggle in persuading the queen to go to Córdoba with her son and grandson, in order to prostrate herself before the caliph, her old enemy, and implore the aid of his arms (958). The proud Navarrese allowed herself to be vanquished by Hasdai—as a Jewish poet of the time expresses himself, "by the charm of his words, the strength of his wisdom, the force of his cunning, and his thousand tricks." Hasdai retained his high position under 'Abd al-Rahman's son and successor, Al-Hakim, who even surpassed his father in his love for science.
Hasdai sent a letter to Empress Helena of Byzantium in which he pleaded for religious liberty to be granted to the Jews of Byzantium. He pointed to his own warm relations with the Muslim Caliph in Córdoba as well as his benevolent attitude towards the Christians of Spain. See http://www.lib.cam.ac.uk/Taylor-Schechter/exhibition.html, T-S J2.71.
Hasdai sent rich presents to the yeshiva of Sura and that of Pumbedita, and corresponded with Dosa, the son of Saadia Gaon. He was also instrumental in transferring the center of Jewish theological studies from Babylonia to Spain, by appointing Moses ben Hanoch, who had been stranded at Córdoba, director of a school, and thereby detaching Judaism from its dependence on the East, to the great joy of the caliph, as Abraham ibn Daud says (Sefer ha-Kabbalah p. 68). Ibn Abi 'UKaibia writes of him: "Hasdai b. Isaac was among the foremost Jewish scholars versed in their law. He opened to his coreligionists in Andalusia the gates of knowledge of the religious law, of chronology, etc. Before his time they had to apply to the Jews of Baghdad on legal questions, and on matters referring to the calendar and the dates of the festivals" (ed. Müller, ii. 50).
Hasdai marks the beginning of the florescence of Andalusian Jewish culture, and the rise of poetry and of the study of Hebrew grammar among the Spanish Jews. Himself a scholar, he encouraged scholarship among his coreligionists by the purchase of Hebrew books, which he imported from the East, and by supporting Jewish scholars whom he gathered about him. Among the latter were Menahem ben Saruq of Tortosa, the protégé of Hasdai's father, and Dunash ben Labrat, both of whom addressed poems to their patron. Dunash, however, prejudiced Hasdai to such a degree against Menahem that Hasdai caused Menahem to be maltreated.