Educated in the major cultural center of Nishapur, and employed at the court of the famous Ghaznavid Sultan Mahmud, Bayhaqi was a highly cultured man, whose magnum opus—the Tarikh-i Bayhaqi, is seen as the most reliable source of valid information about the Ghaznavid era, which was written in an exquisite and vivid Persian prose that would become an ideal model for several eras.
Bayhaqi is praised by modern scholars for his frankness, precision, and elegant style in his book, which he had spent 22 years to write, finishing it in thirty volumes, of which however only five volumes and half of the sixth exist today. Julie Scott Meisami places Bayhaqi among the historians of the Islamic Golden Age.
Bayhaqi was born in the village of Harethabad in Bayhaq in the Khorasan Province, then under the rule of the declining Samanid emirate; in 998, the Ghaznavid ruler Mahmud of Ghazni (r. 998-1030) declared independence from the Samanids, and eventually divided the Samanid state with the Karakhanids, ending the Samanid dynasty. In his youth Bayhaqi studied in the major cultural center of Nishapur, and later in 1020/1 joined the secretariat (dīvān-e resālat) of Mahmud, where he worked as an assistant and pupil under the chief secretary Abu Nasr Mushkan for 19 years.
After Mushkan's death in 1039/40, Mas'ud I (r. 1030–1040) appointed Bayhaqi as minister to Abu Sahl Zawzani, who had succeeded Muskhan as the chief secretary of the empire. Muskhan substantially urged the Sultan that Bayhaqi should be his successor, and the Persian vizier Ahmad Shirazi had also commended Bayhaqi in the Sultan’s attendance. Bayhaqi (who was at that time 46 years old) was supposedly told by Mas'ud I that he was too young to be appointed the new chief secretary.
Zawzani was not as accomplished in the management of the secretariat as his predecessor had been, and his methods were completely dissimilar. Furthermore, Bayhaqi was often a victim of his bad temper, which made the latter send a secret letter of relinquishment of his responsibility to the Sultan, who, however, heartened Bayhaqi to continue serving in his post, whilst ordering his vizier to inform that Zawzani should behave properly towards Bayhaqi at the secretariat. This he did, however; Mas'ud I died shortly afterwards being deserted by his army after a disastrous defeat against the Seljuq Turks, who then conquered Khorasan. Mas'ud's death made Zawzani resume his bad treatment of Bayhaqi once more. Bayhaqi experienced several problems after Mas'ud I's death, probably partly due to his own failings, which he himself often recognizes.