Causes
The reasons for the mutiny revolved mainly around resentment against changes in the sepoy dress code in November 1805. Hindus were prohibited from wearing religious marks on their foreheads and Muslims were required to shave their beard and trim their moustache. In addition General Sir John Craddock, Commander-in-Chief of the Madras Army ordered the wearing of a round hat (resembling that associated with both Europeans and Indian Christians) with a leather cockade in place of the existing turban, a measure which offended both Hindu and Muslim sepoys and went contrary to an earlier warning by a Military Board that sepoy uniform changes should be "given every consideration which a subject of that delicate and important nature required".
These apparently minor changes, intended to improve the "soldierly appearance" of the men, created strong resentment among the Indian soldiers. In May 1806 some sepoys who protested the new rules were sent to Fort Saint George (Madras then, now Chennai). Two of them — a Hindu and a Muslim — were given 90 lashes each and dismissed from the army. Nineteen sepoys were punished with 50 lashes each and forced to seek pardon from the East India Company.
In addition to the military grievances listed above, the rebellion was also instigated by the sons of the defeated Tipu Sultan, confined at Vellore since 1799. Tipu's wives and sons, together with numerous retainers, were pensioners of the East India Company and lived in a palace within the large complex comprising the Vellore Fort. One of Tipu Sultan's daughters was to be married on 9 July 1806, and the plotters of the uprising gathered at the fort under the pretext of attending the wedding. The objectives of the civilian conspirators remain obscure but by seizing and holding the fort they may have hoped to encourage a general rising through the territory of the former Mysore Sultanate
Read more about this topic: Vellore Mutiny