Musa Jarullah Bigiev (Tatar: Муса Ярулла Бигиев; 25 December 1873 – 28 October 1949) was a Tatar Muslim scholar, theologian, philosopher, and publicist. He was one of the leaders of the Jadid movement, an Islamic modernist movement in the Russian Empire. As a controversial reformist thinker, Bigi received the nickname "Luther of Islam" from the scholar, Ottoman Shaykh al-Islam Mustafa Sabri.

After receiving his education in Kazan, Bukhara, Istanbul, and Cairo, he became a political activist for the Ittifaq, the political organisation of the Muslims of Russia. He also taught in Orenburg, wrote journalistic texts and translated classic works into Tatar. After emigrating from the Soviet Union, he travelled Europe and the Near and Far East while writing and publishing.

In modern Tatar, Bigiev's name is written as Бигиев Муса Җарулла, Bigiev Musa Carulla, or Муса Ярулла улы Бигиев, Musa Jarulla ulı Bigiev. He had various names in Arabic; for example, Musa Jarullah ibn Fatima at-Turkistani al-Qazani at-Tatari ar-Rostofdoni ar-Rusi (موسى جار الله ابن فاطمة التركستاني القازانى التاتارى الروستوفدونى الروسى), ibn Fatima at-Turkistani ar-Rostofdoni ar-Rusi (موسى جار الله، ابن فاطمة، التركستاني الروستوفدوني الروسي), ibn Fatima ar-Rusi (ابن فاطمة الروسي), ibn Fatima at-Turkistani al-Qazani ar-Rusi (موسى بن جار الله التركستاني القازاني الروسي), at-Turkistani al-Qazani ar-Rusi (موسى بن جار الله التركستاني القازاني الروسي), or Musa Effendi Jarullah ar-Rusi (موسى أفندي جار الله الروسي).

There is no standardized English transliteration of Bigiev's name; versions include Bigi or Bigeev. His pen name his also variously given as Musa Jarullah, which is the name most contemporary Muslims knew him under, or as Musa Carullah, which is the name mostly used in modern Turkish literature.

Both the date and the place of Musa Bigievs birth are disputed. Opinions for the date include 1870, 1875 or 1873. The place is either the village of Mishar or the city of Novocherkassk. He was born into a middle-class family as the younger of two brothers. After his father was appointed as Akhoond, the family moved to Rostov-on-Don. After the father's early death in 1881, Bigiev's mother, Fatima Hanim Bigiyeva, provided for the education of him and his elder brother Muhammad Zahir Bigiev.

Bigiev spent most of his youth studying at madrasas in Kazan, Bukhara, Samarkand, Mecca, Medina, Cairo (where he attended the Dar al-Ifta al-Misriyyah and was educated by Shayk Muhammad Bakhit al-Muti'i), Damascus, Istanbul and Uttar Pradesh in India, where he studied Sanskrit and the Mahabharata. While he attended many famous universities, he preferred studying on his own while benefitting from the mentorship of different scholars.

In 1904, he returned to Russia, where he married Asma Aliye Khanim, daughter of a merchant and madrasah teacher from Chistopol. Afterwards, he moved to St. Petersburg and attended lectures at the Law faculty of St. Petersburg Imperial University as an auditor, in order to be able to compare Islamic and Western legal systems. He also became good friends with Abdurreshid Ibrahim, the editor of the newspaper Ülfät, in which he published several times.

During the Revolution of 1905, Bigiev became actively involved in the founding of the Muslim political organization, and later party, Ittifaq al-Muslimin, starting with the first Congress of the Muslims of Russia, which was held in Nizhny Novgorod in August. He also participated in the second and third congresses of 1905 and 1906, where he was elected as a member of the central committee of the parliamentary group in the Duma. Bigiev was responsible for providing the protocols of the Ittifaq meetings.