Henry spent many years in India with the Civil Service. Here he met and married Louisa Langrishe in 1890. They had three children.
Posted to Bengal in 1873 he was made Inspector-General of Police in 1891. After secondment to the Transvaal police force he returned to England in 1901, becoming assistant commissioner of the Metropolitan Police. Promoted to commissioner in 1903 he proved an excellent manager and brilliant policeman. However, it was his work on Sir William Herschel’s use of fingerprints for recording illiterate contractors that marked him out. Through correspondence with Francis Galton and practical work with sub-inspectors Aziz-ul-Haque and Hem Chandra Bose, Henry developed this into a form of criminal identification. His system was accepted in India in 1897 and in Britain in 1899. He published Classification and Uses of Fingerprints in 1900 and established the first fingerprint bureau at Scotland Yard in 1902, recording 5155 prints by 1905. After retiring in 1918 he continued this work.
While living in Sheffield Terrace he narrowly avoided assassination by Alfred Bowles. Dropped off from work by his official car he was shot on his doorstep. The reason for the attack was that Scotland Yard had refused Bowles’ request for a cab licence, in hindsight a very wise decision.