Al-Modarresi was born into a distinguished Shia religious family in Karbala in Iraq.
He claims descent from Zayd ibn Ali (died c. 740 AD), the great-great-grandson of the Islamic prophet, Muhammad.
[6] He emigrated to Kuwait with his older brothers in 1971, due to the Bathists anti-Shia sentiment.
[9] Al-Modarresi taught in al-Qaim seminary, which was established by his brother Muhammad-Taqi, in 1980, until it was closed down in 1990.
During his time in al-Qaim, al-Modarresi taught distinguished Saudi activist Nimr al-Nimr and was considered as his mentor.