The son and successor of Malik-Shah I (r. 1072–1092), he reigned during the opening stages of the decline and fragmentation of the empire, which marked the rise of Turkoman atabegates and principalities, which would eventually stretch from Kirman to Anatolia and Syria.

[6][7][8] Berkyaruq was only thirteen at the time of his father's death in November 1092, meaning that there were no princes of age to inherit the vast Seljuk empire.

[11] Malik-Shah's death thus marks the start of the decline and fragmentation of the empire, with amirs and palace elites trying each to gain power by supporting one of his young sons as sultan.

[9] One of Malik-Shah's wives, Terken Khatun, in cooperation with the Seljuk vizier Taj al-Mulk, installed her four-year-old son Mahmud on the throne at Baghdad.

[12] She convinced the Abbasid caliph al-Mustazhir (r. 1094–1118) to have the khutba (friday sermon) read in Mahmud's name, and sent an army under the amir Qiwam al-Dawla Kirbuqa to take Isfahan and capture Berkyaruq.

[11][9] During the chaos that ensued, Malik-Shah's brother Arghun Arslan conquered most of Khurasan (except the city of Nishapur), attempting to establish his own principality in the province.

He sent a second army under his half-brother Ahmad Sanjar in 1097, but before anything occurred Arghun Arslan was killed by one of his own ghulams, due to his brutal treatment of his subjects.

Berkyaruq appointed Sanjar as the vassal ruler (malik) of Khurasan, giving him his own atabeg (Amir Qumaj) and vizier (al-Tughrai).

[17][18][19] Berkyaruq then led an expedition as far east as Tirmidh, where he confirmed the Qarakhanids Sulayman-tegin and Mahmud-tegin as the vassal rulers of Transoxiana.

[20] He also appointed Qutb al-Din Muhammad as the new governor of the Central Asian region of Khwarazm, thus marking the start of the Khwarazmian dynasty.

Sa'd al-Dawla Gawhara'in, the shihna (military administrator) of Baghdad, soon joined Muhammad, which implies that the city was also added to his domain.

[27] En route to Isfahan, he died of tuberculosis at the age of 25 near the town of Borujerd, and was succeeded by his infant son Malik-Shah II.