Léon Odon Marie Anatole de Montesquiou-Fezensac was born on 14 July 1873 in Briis-sous-Forges, Seine-et-Oise.

He was raised in the family chateau of Courtanvaux until the age of ten, then was sent to the Stanislas Catholic school in Paris.

[1] Montesquiou performed his military service as a private soldier from 13 November 1894 to 24 September 1895 in the 115th Infantry Regiment, and was in one of the units designated to witness the degradation of Captain Alfred Dreyfus.

He contributed to the revue grise from 1900, writing firmly nationalistic articles that were later collected into books such as Le Salut public (1901) and La Raison d'État (1902).

By the end of December 1902 was chairman of the board of Action française review, which had just been incorporated as a public limited company.

[2] Montesquiou was among the many early members of the Action Française who were practicing Catholics, and included the art historian Louis Dimier and the essayist Bernard de Vésins.

[2][a] The decision of the Court of Cassation on 12 July 1906 to annul the conviction of Captain Dreyfus caused a renewed surge of anti-Drefusism among the Action française, with Montesquiou playing a leading role.

[2] The League denounced the decision, and violently attacked General Georges Picquart, the new Minister of War.

In April 1907 Montesquiou was officially informed by the Ministry of War that a report on his activity in the Action française had been filed in his dossier as an officer.

On 26 April 1907 Le Gaulois published his open letter to Prime Minister Georges Clemenceau in which he responded to the report by saying he would again put up posters against the rehabilitation of Dreyfus and Picquart.