He succeeded Šagarakti-Šuriaš, who could have been his father, ruled for eight years,[i 1] and went on to wage war against Assyria resulting in the catastrophic invasion of his homeland and his abject defeat.

[3][i 2] According to his eponymous epic, Tukulti-Ninurta I, king of Assyria, was provoked into war by Kaštiliašu's dastardly preemptive attack on his territory, thereby breaching an earlier treaty between their ancestors Adad-nīrāri I and Kadašman-Turgu.

[2] He also reconfirmed a large gift of land on a kudurru that had been provided to Uzub-Šiḫu or -Šipak by the Kassite king, Kurigalzu II (c. 1332-1308 BC) in grateful recognition of his service in an earlier war against Assyria.

[7] Kaštiliašu was captured, single-handed by Tukulti-Ninurta according to his account, who “trod with my feet upon his lordly neck as though it were a footstool”[8] and deported him ignominiously in chains to Assyria.

The victorious Assyrian demolished the walls of Babylon, massacred many of the inhabitants, pillaged and plundered his way across the city to the Esagila temple, where he made off with the statue of Marduk.

After Kaštiliašu's overthrow, however, Kidin-Hutran III, the king of Elam, certainly led two successive incursions into Babylonia, which have been explained as either indicative of his loyalty to the fallen Kassite dynasty or alternatively raiding with impunity to exploit the weakness of the over-extended Assyrians.

[19] It is preserved in heavily damaged late-period tablets, in which Šulgi (2112–2004 BC), the second and most famous king of the third dynasty of Ur, and founder of Nippur, summarizes his achievements.