Musa al Kazim was born in Abwa, a town between Mecca and Medina. His father was Jafar as Sadiq, the sixth Shia Imam, and his mother was a Berber slave named Hamida. As a youngster, he studied under his father who was renowned for his knowledge in the sciences, law and religious studies. Jafar died when Musa was 20. Upon his fathers death, the title of Imam was contested. Some felt that it had passed to his brother Ismail bin Jafar who had predeceased their father, while others felt it belonged to his other brother Abdullah al Aftali.
Despite this controversy, Musa was sucessful at gaining the allegiance of most of the Shia community, cementing himself as the Imam. During Musa's Imamate, the Hashemites were facing persecution from the new Abbasid rulers of Baghdad. Musa was eventually arrested by Harun Rashid and sent to Baghdad to be executed. However, Rashid had a dream at the last minute, and instead freed Musa giving him a thousand dinars and sending him back to Medina. Despite his change of heart, Rashid would continue to regard the descendents of Muhammad as a threat to his rule, and as such, Musa was arrested again and kept in jail for six years. He was poisoned on September 4, 799 while in jail, and his body was put on display so that Harun Rashid could dispel any rumors of Musa still being alive.
He was buried south of Baghdad in what a town that is now named after him, Kazmain.