His reign, lasting only six months, saw a shift in policies, including a more favorable stance towards the House of ʻAlī and the lifting of the ban on pilgrimage to the tombs of Hassan and Hussayn.

Al-Muntasir engaged in military actions against the Byzantines, led by his general Wasif al-Turki, but his sudden death in June 862 resulted in a change of leadership, and al-Musta'in succeeded him as caliph.

[4][5] In late autumn 861, matters came to a head: in October, al-Mutawakkil ordered the estates of the Turkic general Wasif to be confiscated and handed over to al-Fath.

[6][7] They were soon joined, or at least had the tacit approval, of al-Muntasir, who smarted from a succession of humiliations: on 5 December, on the recommendation of al-Fath and Ubayd Allah, he was bypassed in favor of al-Mu'tazz for leading the Friday prayer at the end of Ramadan, while three days later, when al-Mutawakkil was feeling ill and chose al-Muntasir to represent him on the prayer, once again Ubayd Allah intervened and persuaded the Caliph to go in person.

Even worse, according to the historian al-Tabari, on the next day, al-Mutawakkil alternately vilified and threatened to kill his eldest son, and even had al-Fath slap him on the face.

[5][8] According to al-Tabari, a story later circulated that al-Fath and Ubayd Allah were forewarned of the plot by a Turkic woman, but had disregarded it, confident that no one would dare carry it out.

Al-Muntasir, who now assumed the caliphate, initially claimed that al-Fath had murdered his father and that he had been killed after; within a short time, however, the official story changed to al-Mutawakkil choking on his drink.

[13] Although he was suspected of being involved in the plot to kill al-Mutawakkil, he was able to quickly take control of affairs in the capital city of Samarra and receive the oath of allegiance from the leading men of the state.

Included among these were his secretary, Ahmad ibn al-Khasib, who became vizier, and Wasif, a senior Turkic general who had likely been heavily involved in al-Mutawakkil's murder.

[15] Al-Muntasir was lauded because, unlike his father, he loved the house of ʻAlī (Shīʻa) and removed the ban on pilgrimage to the tombs of Hassan and Hussayn.

Following his death, the vizier Ahmad ibn al-Khasib and a small group of senior Turkish commanders met and decided to appoint al-Musta'in as caliph in his stead.

The ascension of al-Musta'in could not be ignored indefinitely by Wasif; having already missed the opportunity to play a role in the selection of the new caliph, he needed to make sure his interests back in the capital were protected.