Ahmad was a son of al-Hasan bin al-Qasim (d. 1639), a brother of the former imam al-Mutawakkil Isma'il.
In the reign of his uncle, in 1658, he led forces that loosely incorporated Hadramaut in the Yemeni kingdom.
He had, however, to fight his cousin and rival al-Qasim who controlled Shaharah, an almost impregnable fortress north of San'a.
The Jews were later allowed to move to Qa'a al-Yahud (the new Jewish Quarter), a suburb situated two kilometers from San'a.
Through mediation of the Ulama (religious scholars), one of these, al-Mu'ayyad Muhammad II, took power.