He was a son of Peroz I and younger brother of Kavad I. Jamasp was installed on the Sasanian throne upon the deposition of the latter by the nobility and clergy.

[1][2] The name is transliterated in Greek as Zamásphēs; Arabic Jāmāsb, Zāmāsb, and Zāmāsf; New Persian Jāmāsp and Zāmāsp.

[8] The main Sasanian cities of the eastern region of Khorasan−Nishapur, Herat and Marw were now under Hephthalite rule.

[9] Peroz' brother, Balash, was elected as shah by the Iranian magnates, most notably Sukhra and the Mihranid general Shapur Mihran.

[11] Sukhra, who had played a key role in Balash's deposition,[11] appointed Kavad I as the new shah of Iran.

[6] Kavad's reclamation of his throne displays the troubled circumstances of the empire, where in a time of anarchy a small force was able to overwhelm the nobility-clergy alliance.