The customary answer to this question is 3:35pm on April 16th, 1853, when a train with 14 railway carriages and 400 guests left Bombay’s Bori Bunder for Thane, with a 21-gun salute. It was hauled by three locomotives: Sindh, Sultan, and Sahib. The journey took an hour and fifteen minutes.
That, however, was just the first commercial passenger service in India. In fact, a few other railways are known to have operated in India prior to 1853, for hauling materials.