Ilyas was appointed governor of Tripoli (Tripolitana) by his brother, Abd al-Rahman ibn Habib al-Fihri, not long after the latter seized power in Kairouan in 745.
In 747, Ilyas tried to crack down on the fledgling Ibadites, a puritanical Kharijite sect strong in the cities of Djerba and Tripoli.
The Ibadites, inspired by the success of their brethren in Hadramut and Oman, revolted under the leadership of their imam al-Harith, and seized control of much of Tripolitana, between Gabès and Sirte, for themselves.
After the victory of the Abbasids in the east in 750, many members of the Umayyad clan fled to Ifriqiya, at the invitation of Abd al-Rahman ibn Habib.
Ilyas continued to serve under his brother, defeating various revolts against Fihrid rule, albeit growing increasingly resentful of the lack of honors that resulted.
Urged on by his vengeful Umayyad wife, Ilyas assassinated his brother Abd al-Rahman ibn Habib in his personal quarters, plunging a dagger into his back while he played with his children.