[2][3] He appears in the aftermath of the Siege of Baghdad and al-Ma'mun's victory in the civil war with his brother al-Amin.
Al-Hasan was appointed by al-Ma'mun as governor and viceroy of an extensive portion of the Abbasid empire, from Jibal and Fars to Iraq, the Hejaz, and Yemen.
[4] In 815 he was one of the chief commanders that put down the Alid uprising of Abu al-Saraya al-Sari ibn Mansur in Iraq, defeating the rebel forces at al-Mada'in in late May,[5] recapturing Wasit,[6] and finally capturing Basra from its cruel Alid governor, Zayd ibn Musa al-Kadhim.
[7] In the aftermath, he sent a number of his commanders to suppress the offshoots of the uprising in the Hejaz, under Isa ibn Yazid.
Although both Ali and the other imprisoned commanders denied their involvement, al-Ma'mun had them executed, and their severed heads sent to al-Hasan ibn Sahl in Iraq along with news of his brother's fate.