Hearsey enlisted in the British Indian army in 1808. He was promoted to lieutenant in 1809, captain in 1819, major in 1833, lieutenant colonel in 1838, brevet colonel in 1849, colonel in 1852, major general in 1854, and lieutenant general in 1862. In 1857, he was the commanding officer at
Barrackpore when
sepoy Mangal Pandey attempted to start a mutiny and was threatening to shoot British officers. When confronted by Maj.-Gen. Hearsey and ordered to surrender, Pandey shot himself but survived. He and another Indian sepoy—who had refused to arrest Pandey—were later hanged, despite Pandey's pleas that he had been under the influence of
opium and
bhang at the time of his actions. The incident contributed to the
Indian Rebellion of 1857. In July 1857, he was appointed a
Knight Commander of the Order of the Bath for his role in suppressing the rebellion. ==Naturalist==