Muhammad ibn Zayd is the younger brother of Hasan ibn Zayd, an Alid who had founded Zaydid rule over Tabaristan in 864.
Nothing is known of his early life.
Muhammad is mentioned during Hasan's rule as being captured by Ya'qub al-Saffar during the latter's 874 invasion, but released at Gurgan when Ya'qub withdrew in 876.
After a brief visit to Tabaristan to see his mother, he had returned to Gurgan as an assistant to Hasan's brother-in-law, Muhammad ibn Ibrahim.
The Zaydids had ben expelled from Gurgan by the Tahirid general Ishaq al-Sari in spring 877, but soon recovered it.
In 880, Muhammad also suppressed the rebellion of Rustam ibn Qarin, a member of the native Bavandid dynasty that rules the mountains of eastern Tabaristan and opposes the Zaydids.
He then suppressed a rebellion in Gurgan headed by another Alid, Hasan ibn Muhammad ibn Ja'far al-Aqiqi, and probably continued to govern the province in his brother's name until the latter's death on January 6, 884.
Power in Tabaristan is usurped upon Hasan's death by his brother-in-law, Abu'l-Husayn Ahmad ibn Muhammad, who proclaims himself as the legitimate emir due to Muhammad's absence in Gurgan.
Muhammad is prevented from returning to Tabaristan straight away by a mutiny by his Daylamite troops, and is able to regain control of Gurgan itself only through the aid of the former Tahirid general and now ruler of Khurasan, Rafi' ibn Harthama.
Muhammad is able to finally return in October 884 to Tabaristan, seize the capital Amol, and behead the usurper.
Muhammad assumes the same regnal name as his brother, al-Da‘ī ila‘l-Haqq ("He who summons to the Truth"), and is known as al-Da‘ī al-Saghīr ("the Younger Missionary") in contrast to Hasan (al-Da‘ī al-kabīr, "the Elder Missionary").
He is also found in some sources as al-Qa’im bi al-Haqq ("Upholder of the Truth").
Muhammad now attacks Rustam, who had supported the usurper Ahmad, and drives him from his domains to seek refuge at the Saffarid court.
Saffarid mediation enables Rustam to return.
