In 1827, he entered the Addiscombe Military Seminary and the service of the East India Company. He joined the Bengal Artillery in 1828, and in 1829 arrived in Calcutta. In 1837 he was appointed to the horse artillery and promoted Lieutenant. Two years later, he was appointed Commissary of Ordnance to the Cabul field force. In January 1842, During the First Anglo-Afghan War, Eyre and his family were captured by Akbar Khan. During nearly nine months in captivity, Eyre kept a diary describing his experiences, illustrated by the sketches of other officers and ladies. The manuscript was smuggled out to a friend in British India and was then published in England as "Military Operations at Cabul" (1842). The Eyre family were rescued by Sir George Pollock in September 1842. In 1844 Eyre was appointed to command the artillery of the new Gwalior contingent. He was responsible for the relief of the Siege of Arrah. He took part in the Relief of Lucknow, during the Indian Rebellion of 1857. He was promoted Lieutenant Colonel that year and brevet Colonel the following year.