After the dismissal of Jawhar as-Siqilli in 979 Ya'qub ibn Killis was appointed vizier by al-Aziz, a position he held until his death in 991.
At a young age he came with his father to Egypt, where he started his political life at the court of Kafur, the power behind the throne of the Ikhshidid regime.
This aroused the jealousy of his rival, the vizier Ibn al-Furat, who began to seek a way to eliminate him.
It is said that Ya'qub bribed the jailor and absconded to Ifriqiya, where the Fatimid Caliph al-Mu'izz ruled.
During the last years of the reign of al-Mu'izz, and the first two years of the period of his successor al-Aziz, (975-996), due to toil, honesty and intelligence of Ya'qub ibn Killis, this position became firm and stable, so much so that in 977-78 al-Aziz appointed him as Wazir al-Adjall (Chief Minister).
During his tenure as vizier, Ya'qub ibn Killis established various departments anew for the administration of the state, promoted agriculture, reformed trade and stabilised the currency, by which the country began to flourish and revenue of provinces increased.
Besides, he was at his palace lecturing every Friday night on different subjects, where judges, theologians, grammarians, traditionalists and poets used to gather to hear him.
At Al-Azhar he gave vent to religious education and upon his instructions a University was established in Jama-e-Azhar, which exists until today.
Ya'qub ibn Killis was an efficient vizier and introduced many reforms, as a result of which the public was not burdened and treasury was full.
Al-Aziz, had given him wide powers and he was also drawing a good remuneration from the Treasury with a high position in the government.
In the month of Ramadhan besides judges and prominent persons, nominal and general public also used to take advantage of his favour.