He eventually grew angry over this state of affairs and sided with a faction seeking to murder Izz al-Din's vizier, who had a large amount of influence over the malik.
By the end of the year, however, Qutb al-Din had defeated the invaders, forced his father into exile and later received the latter's renunciation of the throne.
Over the course of his first year in power, he worked at consolidating his rule in Sistan; he led an army against the town of Uq and killed many of the local landowners who had risen in opposition to him.
In the meantime, the amir Timur had begun his expansion into Afghanistan and Persia, forcing the Kartid dynasty of Herat into submission.
After building a pyramid of human skulls out of the slain Mihrabanid soldiers, the Timurid army forced its way into Shahr-i Sistan and Qutb al-Din was imprisoned.