Henry Craven St. John was born in 1837 in the Ross and Cromarty district of Scotland, the son of Charles William George St. John and Anne Gibson and a great grandson of Frederick St John, 2nd Viscount Bolingbroke. He entered the Royal Navy in 1852 as a midshipman on the Cumberland first and later on the Nankin, aboard which he become an acting Lieutenant in
While on duty on the Chinese Coast, his main task was to deal with the numerous pirates operating near Hong Kong in the aftermath of the Taiping Rebellion (1850-1864). He appeared to have been extremely successful in this endeavour, and in July 1866 he was promoted commander at the age of 29, and recalled to the UK. The burghers of Hong Kong presented him a scroll connveying their deepest gratitude.
In 1873 Henry Craven St John was promoted to captain of HMS Sylvia, a Cormorant class surveying vessel commissioned to sail the seas around China and Japan mapping out the coastline, 'for arduous surveying work in Japanese waters'. He then became commanding officer of the Central battery ship HMS Iron Duke in August and held the office of Naval Aide-de-Camp to HM Queen Victoria between 1887 and 1889. In 1889 Rear-Admiral St John was promoted to 'flag rank' and in 1891 succeed Rear-Admiral James E. Erskine as Senior Officer on the Coast of Ireland. Admiral St. John retired from active service in 1901.
St. John had a great interest in natural history, as his works and some of his drawings suggest. In 1880 he published a book entitled Notes and sketches from the wild coasts of Nipon, with chapters on cruising after pirates in Chinese waters (Edinburgh, David Douglas, 1880) and he also edited and published his father's zoological notebooks on Scotland, Charles St. John's note books 1846-1856, (Edinburgh, David Douglas, 1901).
Henry Craven St John died in 1909.