[2] Hennion was born in Gommegnies in 1862, to Joseph Ghislain Hannion, a farm labourer, and Marie-Catherine Basilaire and he was educated at Lycée Le Quesnoy.

Hennion had a rapid rise through the force, and was moved into intelligence work where he investigated organisations intent on over-throwing the Third Republic.

Hennion also thwarted several attacks against political figures and the state, including the 1899 coup d'état by Paul Déroulède, and was dispatched with additional troops to quell unrest in Rennes during the second Dreyfus trial.

He was in post for too short a period to be totally effective but he continued the reforms of his predecessor dividing the police force into three main departments: judicial, intelligence and policy agenda.

[9] For his services in the French Army, Hennion was awarded the Colonial Medal, was made a Knight of the Order of Nichan Iftikhar and an Officier de la Légion d'honneur.