He was the first of a series of Iraqi Christian officials who would come to play a significant role in the Caliphate's administration during the 9th century.
Fadl began his career in the reign of Harun al-Rashid (r. 786–809) as a retainer of Harthama ibn A'yan, at the time head of the caliphal bodyguard.
His administrative talent brought him to the attention of Harun, who appointed him a secretary in the diwan al-kharaj (the "Bureau of the Land Tax").
In September 833, he was appointed as vizier with wide-ranging powers, but his attempts to limit expenditure, and especially the Caliph's largesse to his courtiers, brought about his dismissal in February 836.
He continued to serve Mu'tasim and his successors as an advisor on taxation issues until his death in 864, aged about 90.