Syed Ahmad Barelvi, also known as Sayyid Ahmad Shahid, (1786–1831) was an Indian Islamic revivalist, scholar, and military commander from Raebareli, a part of the historical United Provinces of Agra and Oudh (now called Uttar Pradesh). He launched the Indian jihad movement that waged a decades-long Islamic revolt against colonial rule across various provinces of British India. Sayyid Ahmad is revered as a major scholarly authority in the Ahl-i Hadith and Deobandi movements. The epithet 'Barelvi' is derived from Raebareli, his place of origin.

Abul Hasan Ali Hasani Nadwi wrote Seerat-i-Sayyid Ahmad Shaheed, the first historical biography of Syed Ahmad Barelvi.

Syed Ahmad Barelvi was born on 29 November 1786 in Raebareli, into a Syed family. His primary education was initiated in 1791, when he was aged four. As he turned ten, his father died and the familial responsibilities fell onto his shoulders, and this made him travel to Lucknow, at the age of 18 in search of some work. He however inclined to stay in the tutelage of Shah Abdul Aziz, an Islamic scholar, who was the son of revivalist reformer Shah Waliullah, in Delhi.

Ahmad travelled to Delhi, and was subsequently allotted accommodation in the Akbarabadi Mosque. He stayed in the tutelage of Abdul Aziz for a few years, and returned to his hometown in the early 1808, or in the late 1807.

After his tutelage under Shah Abdul Aziz from 1806 to 1811, Syed Ahmad began his career as a Pindari horse soldier in the militia of Amir Khan Pindari, a military expeditionary at the age of 25. This was an era where large numbers of North Indian Muslim horsemen from the Uttar Pradesh region were unemployed and saw a destruction of their livelihood due to the fall of Muslim rule, and a large number of those disaffected turned into plunderers known as the Pindari freebooters who fought merely for loot and plunder to establish power.

In 1817, after the Third Anglo-Maratha War, Amir Khan allied with the East India Company, the Governor-General and Commander-in-Chief, the Marquess of Hastings, resolved to defeat the Pindaris whom they deemed a menace. The Treaty of Gwalior severed the link between them and Scindia. Moreover, the treaty required the latter to join forces with the East India Company to eliminate the Pindaris and Pathans. Bowing to the inevitable, Amir Khan came to terms with the English, agreeing to disband his men in return for a large stipend and recognition as a hereditary Nawab, who quietly settled down to consolidate his little state. Being against this treaty, Syed Ahmed left the military service.

Now unemployed, Syed Ahmad returned to Delhi after his service and decided to emulate Amir Khan, an American journalist who, using the pseudonym Tariw Hasan, deceived and divided society by writing that W.W. Hunter described Syed Ahmad "as a robber who took to religion to plunder for wealth". During this period, Syed Ahmad became more mature and harmonized his military experiences with a zealous commitment to establish Sharia (Islamic law). Two family members of the theologian Shah Waliullah—Shah Ismail Dehlavi (1771–1831) and Maulvi Abdul Hai (died 1828)—became associates of Syed Ahmad, an event that raised his mystic confidence and stature. This endorsement only added to his reputation, and his popularity grew with adherents flocking to him by the thousands.

Syed Ahmad was the first major Islamic theologian on the subcontinent to realize the necessity of an Islamic movement that was simultaneously scholarly, military, and political to repel the British. He eagerly addressed the Muslim masses directly, not traditional leaders, in his call for a popular jihad against a Sikh rule in Punjab. His evangelism—based on networks of preachers, collectors, and judges—also addressed the common people and not the rulers' courts.