Zahir al-Din was the nephew of Yahya Karawi. After his uncle's murder in 1355 or 1356, the partisans of Wajih ad-Din Mas'ud attempted to take control of the government and install Mas'ud's son Lutf Allah as head of state. They were, however, dispersed by Haidar Qassib, who then declared Zahir al-Din as ruler.

In the meantime, some of Lutf Allah's supporters had escaped from Sabzewar. Lutf Allah's atabeg Nasr Allah soon rebelled in Esfarayen. Haidar Qassib encouraged Zahir al-Din to move against the rebels but his advice was ignored. He then deposed Zahir al-Din and took control of Sabzewar himself.

• Roemer, H. R. "The Jalayirids, Muzaffarids and Sarbadars." The Cambridge History of Iran Volume 6: The Timurid and Safavid Periods. Edited by Peter Jackson. New York: Cambridge University Press, 1986. ISBN 0-521-20094-6
• Smith, Jr., John Masson. The History of the Sarbadar Dynasty 1336–1381 A.D. and Its Sources. The Hague: Mouton, 1970. ISBN 90-279-1714-0