After the war Darnand worked as a cabinetmaker before establishing his own transport company in Nice. He became interested in politics and was a supporter of the royalist group Action Francaise. In the 1930s he moved further to the right and developed neo-fascist political views.
Darnand volunteered for military duty at the beginning of the Second World War and fought bravely along the Maginot Line. He was taken prisoner in June 1940, but managed to escape and went to live in Nice.
In July 1941 Darnand established the right-wing military group, Service d'Ordre Legionnaire. The organization supported Henri-Philippe Petain and the Vichy government and offered its help to round up Jews and to fight against the French Resistance.
In January 1943 the Service d'Ordre Legionnaire was transformed into the Milice the secret police in Vichy. Darnand was given the Waffen SS rank of Sturmbannfuehrer and took a personal oath of loyalty to Adolf Hitler.
Darnand expanded the Milice and by 1944 it had over 35,000 members. The organization played an important role in investigating the French Resistance. Like the Gestapo, the miliciens were willing to use torture to gain information.
In December, 1943, Darnand was named secretary-general for the maintenance of order and head of police in Vichy. The following month he was made secretary of the interior.
After the D-day landings took place the Maquis and other resistance groups emerged to help in the liberation of their country. Darnand fled to Germany where he served as a member of Petain's exiled government at Sigmaringen. Joseph Darnand was eventually captured by the Allies and was returned to France where he was tried and executed in 1945.