The son of the distinguished military leader Khazim ibn Khuzayma, he inherited a position of privilege and power, and served early on in high state offices.

Through Khazim, the family achieved a prominent place among the Khurasaniyya, the Khurasani soldiers who had come west during the Revolution and formed the main power-base of the early Abbasid regime.

Although Khuzayma had been a staunch supporter of al-Hadi, the Caliph's decision to strip his brother Abdallah from the post of sahib al-shurta probably alienated him.

Khuzayma reportedly gathered and armed 5,000 of his own followers, dragged the young prince from his bed and forced him to publicly renounce his claims in favour of Harun.

As the siege progressed, the elites' support for al-Amin began to waver, and in September 813, Khuzayma was contacted by al-Ma'mun's general, Tahir ibn Husayn.

The talks bore fruit, and on the night of 21 September, Khuzayma's servants cut the main bridge over the Tigris linking the eastern and western quarters of Baghdad.