Rustam V is first mentioned as the leader of a group of nobles which plotted to overthrow Ardashir and crown him as the ruler of the Bavand dynasty.
In 1205, Ardashir died—about the same time, Sharaf al-Muluk died, and thus the succession passed to Rustam V, who was freed from prison and brought to the throne at the Bavandid capital of Amol.
However, his brother Rukn ad-Dawla Qarin, claimed the throne for himself and went to Khwarazm, where he requested aid from the Khwarazmian king Muhammad II.
Muhammad II agreed to help him, and ordered his brother, Ali-Shah, who was the ruler of Damghan and Bastam, to invade Rustam's domains, which he did.
The brothers, however, made a peace treaty, which resulted in Rukn ad-Dawla Qarin receiving the inheritance of Sharaf al-Muluk.