After serving in the United Provinces of Agra and Oudh in the public works department, St John volunteered for work inPersia. This mission was mainly to establish a telegraph line between Persia and India. This mission, along with Patrick Stewart, was meant to lay a cable in the Persian Gulf and a land cable line for telegraphic link to Bosporus. Stewart and his brother Champain had already worked on a survey in Turkey. St John worked on the expedition under Captain Murdoch Smith, RE. He later took charge of the line from Teheran to Bashahr, and during this time a second telegraph line was added. He went home in May 1867 and he was then sent to Abyssinia to organize telegraph lines for the war. This line was 200 miles from the coast and the work led to his promotion. Towards the end of 1868 he returned to Persia and he remained here till 1871. In October 1871, St John was sent to Baluchistan for the survey of the Perso-Kelat frontier. He returned to England in October 1872 and worked on preparing maps at the India Office. These maps were based on longitudes of the Persian telegraph stations fixed in co-operation with General James Walker of the Indian Trigonometric Survey, Captain William Pierson, RE, and Lt Stiffe, IN. St John published his notes in the Narrative of a Journey through Baluchistan and Southern Persia. He returned to India in 1875 and became principal of the Mayo College in Ajmer. After August 1878 he became part of the staff of Sir Neville Chamberlain's mission to Kabul. He then became chief political officer to the KandaharField Force, becoming later Resident in Kandahar. An attempt was made on his life during a trip in southern Afghanistan. He was also posted on special duty in Kashmir, acting resident in Hyderabad, resident in Kashmir, agent to the governor-general at Baroda, resident at Mysore and chief commissioner in Coorg. He was later recalled from southern India to Baluchistan. He died in Quetta of pneumonia after an attack of influenza.
Natural history
During all his time in Abyssinia, Persia and Baluchistan St John took a keen interest in natural history and hunting. His personal notes from the Persian border commission expedition of 1871 are included in the zoology report of the expedition prepared by William Thomas Blanford. Blanford's own account includes notes on St John's experiences with lions in Persia, while another account is provided of him chasing a tiger that threatened a colleague. St John also corresponded with ornithologists in the region, including Allan Octavian Hume. A species of woodpecker and a species of snake are both named after him.
Death
St John died on 3 June 1891 in Quetta of pneumonia after an attack of influenza during a recurrence of the 1889–90 pandemic.
