Joined the Bengal Army as Assistant Surgeon on Sept 18th, 1799, being promoted to Surgeon on March 5th, 1813, and to Superintending Surgeon on June 24th, 1826. He became a member of the Calcutta Medical Board on July 23rd, 1833, and President on Feb 25th, 1834. He saw active service in the Third Maratha or Pindari or Dekkan War in 1817-1818. Through his many years of active service in the East he proved an energetic and valuable public servant. He played his part as a medical officer in Indian affairs. Thus he was Medical Attendant to Lord Metcalfe’s Embassy, to Runjeet Singh, ruler of the Punjab and annexor of Cashmere, and personally received many evidences of his chief’s esteem. In the campaign in 1817 he was attached to the Army under the command of the Marquis of Hastings, when the cholera is said to have made its disastrous appearance. He retained to the last a vivid recollection of all the circumstances connected with the onset of this pestilence, which has since then devastated large areas. Langstaff returned to England in good health, having retired on July 23rd, 1838, and lived for many years in the bosom of his family. At the time of his death he was one of the oldest medical officers of the Bengal Presidency. He died of apoplexy at his house, 9 Cambridge Square, on Dec 6th, 1856.