Ali bin Salah ad-Din was a son of the preceding imam
an-Nasir Muhammad Salah ad-Din who had held extensive power in highland Yemen. He grew up in
San'a, the most important city of the realm. After an-Nasirs sudden demise in 1391, no less than four claimants to the imamate appeared, foremost among them the learned
al-Mahdi Ahmad bin Yahya. The young Ali eventually prevailed. He was proclaimed imam under the name al-Mansur Ali, with the support of the scholars and population of San'a. However, a rival imam called
al-Hadi Ali had some support in the northern parts of the Zaidi territory from 1393 to 1432. Due to the unrest, al-Mansur Ali had to travel frequently to trouble spots. He had to fight hard to gain control over
Sa'dah, the traditional centre of Zaidi power in the north. Various strongholds of the
Tayyibi Isma'ili sect were taken, and their leader
Ali Shams al-Din II was forced out of
Dhu Marmar, a fortress to the east of San'a.
Idris Imad al-Din with the
Rasulid dynasty Sultan al-Malik al-Zahir (r. 1428–1439) repeatedly fought against the Zaydi imam al-Mansur Ali (r. 1391–1436), and recaptured numerous fortresses from Zaydi control. In Zaidi
historiography, the imam is celebrated as a
mujaddid bi-sayfihi, a warlike restorer. That his bellicose exploits sometimes afflicted other Zaidi
Muslims did not detract from his reputation. Al-Mansur Ali's rule over
San'a was never in danger, but in 1395 he sacked the
qadi in the city, who had been found to correspond with the
Rasulid Dynasty in the lowland. Two years later he made a diplomatic foray when he sent offerings to the Rasulid Sultan al-Ashraf Isma'il I in
Zabid. The offerings consisted of "five loads of articles esteemed as rarities, and five head of horses of good lineages". ==Later reign and death==