Muḥammad Mahdī Shams al-Dīn (Arabic:محمد مهدی شمس الدین) (b. 1354/1936 – d. 1421/2001) was a religious scholar, political theoretician and the chairman of the Supreme Islamic Shi’a Council in Lebanon. He began his scientific and political activities in Najaf under Al-Sayyid Muhsin al-Hakim and Ayatullah al-Khoei. The cooperation with al-Sayyid Muhammad Baqir al-Sadr and Muhammad Husayn Fadl Allah in founding al-Da’wa Party and the al-Adwa’ magazine was among his most important political activities. In 1395/1975, Shams al-Din accepted the deputyship of the Supreme Islamic Shi’a Council whose director was Imam Musa al-Sadr. After Imam Musa al-Sadr disappeared in 1398/1978, Muhammad Mahdi Shams al-Din accepted the chairman position of this Council and in 1414/1993, he was officially elected as the director of the Supreme Islamic Shi’a Council in Lebanon.