Al-Jawad was born on April 12, 811, in Medina (then part of the Abbasid Empire). He was born to his father, Ali al-Reza and a mother whose name and background is not entirely known. According to Kulaini, his mother was a bondmaid from Nubia named Habibi. However, some say that she was Khaizaran, a girl from the Byzantine Empire. Others believe she belonged to the household of Maria al-Qibtiyya, who was the slave mother of Muhammad's young son Ibrahim.
Al-Jawad's father, Ali al-Reza, expected his son to take the position of Imamate after him. When al-Jawad was four, his father received a summons from the Abbasid Caliph, al-Ma'mun, asking him to be al-Ma'mum's successor. Al-Reza left the four-year-old al-Jawad behind in Medina to respond to the summons. The Shiites questioned whether a child of that age could take on his father's responsibility as an Imamate if something happened to his father. In response, al-Reza used to tell the story of Jesus, who had become a prophet at a younger age.
Al-Jawad's age at the time of his father's death in Korasan is unknown, although probably between seven and nine. With his father's death, al-Jawad became a young Imam. According to Shia beliefs, al-Jawad acted like an adult and possessed extraordinary knowledge. Shia beliefs liken this to Jesus, who was called to leadership and his prophetic mission while still a child.
Accounts differ as to al-Reza’s death and subsequent events. One account states that al-Ma'mun poisoned al-Reza, and then summoned al-Jawad to Baghdad in order to marry his daughter, Ummul Fadhl. This apparently provoked strenuous objections by the Abbasids. According to Ya'qubi, al-Ma'mum gave al-Jawad one hundred thousand Dirham and said, "Surely I would like to be a grandfather in the line of the Apostle of God and of Ali ibn Abu Talib."
Another account states that al-Ma'mum's first meeting with al-Jawad was coincidental. According to this account, al-Ma'mun was hunting when he happened upon a group of boys including al-Jawad, who were playing. When al-Ma'mun's horsemen approached, the boys ran away, except al-Jawad. This prompted al-Ma'mun to stop his carriage and ask, "Boy, what kept you from running away with the others?" Al-Jawad replied, "The road was not so narrow that I should fear there would not be room for you to pass and I have not been guilty of any offence that I should be afraid and I considered that you were the sort of man who would not injure one who had done no wrong."
Shiite traditions say that that the Caliph was delighted and after he traveling a short distance, one of his hunting birds brought him a small fish. Al-Ma'mum hid the fish in his fist, returned and asked al-Jawad: "What have I in my hand?" Al-Jawad responded: "The creator of living things has created in the sea a small fish that is fished by the falcons of the kings and caliphs to try with it the progeny of al-Mustafa. Shiite tradition says that Al-Ma'mun was pleased with this answer and asked the child about his lineage. Soon after, the Caliph called a large gathering, during which al-Jawad was asked many questions and astonished everyone with his judgment and learning. After this, al-Ma'mun formally gave al-Jawad his daughter in marriage.
According to Shiite beliefs, Yahya ibn Aktham, the Chief Justice of the Abbasid Empire, was present at al-Ma'mun's assembly and wanted to try al-Jawad in al-Ma'mun's presence. He did so by asking a question concerning atonement for a person who hunts game while dressed in pilgrimage garb (Ihram). In response, al-Jawad asked first "whether the game killed was outside the sanctified area or inside it; whether the hunter was aware of his sin or did so in ignorance; did he kill the game on purpose or by mistake, was the hunter a slave or a free man, was he adult or minor, did he commit the sin for the first time or had he done so before, was the hunted game a bird or something else, was it a small animal or a big one, is the sinner sorry for the misdeed or does he insist on it, did he kill it secretly at night or openly during daylight, was he putting on the pilgrimage garb for Hajj or for the Umrah?..." This apparently astonished the Abbasid who were critical of al-Ma'mun's decision.
During the next annual pilgrimage (Hajj), prominent men from around the Islamic world came to Medina to see al-Jawad and another assembly was held. These men were skeptical of al-Jawad's youth and whether he truly was the Imamate). Shiite belief holds that the boy eliminated their doubts. Kulaini recounted that the superintendent of the Shrine gave al-Jawad a test that "lasted for several days, in which he answered thirty thousand questions to their great amazement!