During his stay in the company he spent about a year in Gafsa, a prison camp located in the town of the same name in Tunisia.
The publication of Les Pharisiens (1890), in which he harshly attacks Édouard Drumont and other anti-Semites, won him the friendship of Bernard Lazare.
Between 1893 and 1905, Darien traveled frequently to other countries, especially Belgium, Germany and England, residing for long periods in London.
There he would meet his first wife, Suzanne Caroline Abresch, daughter of German parents, a year older than him.
His most important work is Le Voleur, published posthumously and taken to the big screen by Louis Malle in 1967.