Imam Ja'far ibn Muhammad, the son of the fifth Imam, was born in 83/702. He died in 148/765 according to Shi'ite tradition, poisoned and martyred through the intrigue of the Abbasid caliph Mansur.After the death of his father he beacame Imam by Divine command and decree of those who came before him.

  During the imamate of the sixth Imam greater possibilities and a more favorable climate existed for him to propagate religious teachings.This came about as a result of revolts in Islamic Lands, especially the uprising of the Muswaddah to overthrow the Umayyad caliphate, and the bloody wars which finally led to the fall and extinction of the Umayyads.The greater opportunities for Shi'ite teachings were also a result of the favorable ground the fifth Imam had prepared during the twenty years of his imamate through the propagation of the true teachings of Islam and the sciences of the Household of the Prophet.
The Imam took advantage of the occasion to propagate the religious sciences until the very end of his imamate, which was contemporary with the end of the Umayyad and beginning of the Abbasid caliphates. He instructed many scholars in different fields of the intellectual and transmitted sciences, such as  Zorarah,Muhammad ibn Muslim, Mu'min Taq, Hisham ibn Hakam, Aban ibn Taghlib, Hisham ibn Salim, Hurayz, Hisham Kalbi Nassabah, and Jabir ibn Hayyan, the alchemist.
Even some important Sunni scholars such as Sufyan Thawri, Abu Hanifah,the founder of the Hanafi school of law, Qadhi Sukuni, Qadhi Abu'l-Bakhtari, and others, had the honor of being his students. It is said that his classes and sessions of instruction produced four thousand scholars of hadith and other sciences. The number of traditions preserved from the fifth and sixth Imams is more than all the hadith, that have been recorded from the Prophet and the other ten Imams combined.

  Toward the end of his life the Imam was subjected to severe restrictions placed upon him by the Abbasid caliph Mansur, who ordered such torture and merciless killing of many of the descendants of the Prophet who were Shi'ite that his actions even surpassed the cruelty and heedlessness of the Umayyads.
At his order they were arrested in groups, some thrown into deep and dark prisons and tortured until they died, while others were beheaded or buried alive or placed at the base of or between walls of buildings, and walls were constructed over them.Hisham, the Umayyad caliph, had ordered the sixth Imam to be arrested and brought to Damascus. Later, the Imam was arrested by Saffah, the Abbasid caliph, and brought to Iraq. Finally, Mansur had him arrested again and brought to Samarrah where he had the Imam kept under supervision, was in every way harsh and discourteous to him, and several times thought of killing him. Eventually the Imam was allowed to return to Medina where he spent the rest of his life in hiding, until he was poisoned and martyred through the intrigue of Mansur.Upon hearing the news of the Imam's martyrdom, Mansur wrote to the governor of Medina instructing him to go to the house of the Imam on the pretext of expressing his condolences to the family, to ask for the Imam's will and testament and read it. Whoever was chosen by the Imam as his inheritor and successor should be beheaded on the spot. Of course the aim of Mansur was to put an end to the whole question of the imamate and to Shi'ite aspirations. When the governor of Medina, following orders, read the last will and testament,he saw that the Imam had chosen four people rather than one to administer his last will and testament: the caliph himself, the governor of Medina,'Abdullah Aftah, the Imam's older son, and Musa, his younger son. In this waythe plot of Mansur failed.