He belonged to the Qasimid family, descended from the Islamic prophet Muhammad, which dominated the Zaidi imamate of Yemen in 1597–1962.
[3] The German explorer in Danish service, Carsten Niebuhr, visited Yemen in 1762–1763 at the head of a scientific expedition.
In a subsequent interview, Niebuhr was allowed to show the imam their scientific instruments, and al-Mahdi Abbas posed several questions about European manners, commerce and learning.
At the same time, writs then issuing from the king forbade Jews in the city from building their houses higher than fourteen cubits (about 7.5 meters; 24.8 feet).
As for the king's jurisdiction over outlying districts, Niebuhr related that a number of areas in Yemen were autonomous or independent of imamic rule by this time: Al-Mahdi Abbas reportedly preserved the shrunk borders of the Zaidi state vigorously.
In spite of the autonomous position of the Hashid and Bakil tribes, the imam kept several regiments of tribesmen, and paid them better than others.
Under al-Mahdi Abbas the annual revenue again rose to 500,000 riyals, still far below the record years before the 1720s, which had been conditioned by the lucrative coffee trade.