He established a number of schools and medical clinics throughout southern Lebanon, many of which are still operation today.

Sayyed Sadr was also the founder of the first armed resistance in Lebanon against the Israeli occupation, under the name Lebanese Resistance Brigades Movement, Arabic for Amal Movement.

Imam Sadr was born in the holy city Qom, Iran in 1928 to the prominent Sadr family of theologians. His father was Ayatollah Sadr al-Din al-Sadr, while Ayatollah Muhammad Baqir al-Sadr was his cousin. He attended his primary school in his hometown and then moved to the Iranian capital Tehran where he received in 1956 a degree in Islamic Jurisprudence and Political Sciences from Tehran University. He then moved back to Qom to study theology. Eventually he left Qom for Najaf to study theology under Ayatollah Sayed Muhsin al-Hakim and Ayatollah Sayyed Abul Qasim Khou'i. The Sadr family is originally a Lebanese family, and in 1960 Musa al-Sadr accepted an invitation to become the leading Muslim Shi'ite figure in the Lebanese southern city of Tyre. He was a vocal opponent of Israel. In 1969 he was appointed as the first head of the Supreme Islamic Shi'ite Council, an entity meant to give the dacades-long oppressed Shi'ites more say in government. In 1974 he founded the Movement of the Disinherited to press for better economic and social conditions for the Shi'ites.

Libyan authorities claimed that the Sadr, Yaacoub and Badreddine had left Tripoli for Rome, as Ghaddafi refrained from addressing the issue with then Lebanese president Elias Sarkis. An investigative panel was formed to carry out a fact finding mission in Tripoli and Rome, but Libya refused to receive the panel. Investigators concluded that Imam Sadr and his companions had never left Libya and did not check into Italy. Rome conducted two rounds of investigations into the case and authorities concluded that Libyan claims were baseless. For their part, Lebanese authorities considered the disappearance of the Imam and his companions as a crime against the state's internal security and took legal action. On the 30th of August 2001, Amnesty International issued its first report on the disappearance of Imam Sadr and his companions and stressed allegations that they had left Tripoli contradict the outcome of the Italian investigation.

Imam Sadr left Beirut's international airport for an official visit to meet Ghaddafi in Tripoli on the 25th of August 1978, accompanied by Sheikh Mohamad Yaacoub and journalist Abbas Badreddine. According to reports, the trio stayed in the "Shate' Hotel" in Tripoli, however the Imam's visit was not mentioned in Libyan media and every contact with him was cut. Witnesses said that they saw the Imam and his two companions leave the hotel in an official convoy on the 31st of August, the date set for their meeting with Ghaddafi. The Libyan president however denied the meeting ever took place, even though reports say that he confirmed the date was set on the 31st of August at 1:00pm. The same reports said that the meeting did take place and deep differences between Ghaddafi and the Imam surfaced pertaining to the crisis in Lebanon. They added that Kings and rulers intervened in vain to sort out the differences. Sayyed Sadr and his companions disappeared and they were never heard of until this very day.