He was the son of marquis Henri Charles Louis Boniface de Castellane (1814–1847), deputy for Cantal, and his wife Pauline de Talleyrand-Périgord (1820–1890), and was a member of the House of Castellane.

His older sister, Marie de Castellane, was married to Prince Antoine Radziwiłł, a grandson of Prince Antoni Radziwiłł and Princess Louise of Prussia.

[3] Antoine studied at the minor seminary of La Chapelle-Saint-Mesmin, taught by Mgr Félix Dupanloup, bishop of Orléans.

[4] He served in the Franco-Prussian War under marshal Bazaine and was imprisoned with him in Metz whilst prince Frederick-Charles of Prussia (one of his cousins by marriage) celebrated the establishment of the German Empire at the Château de Rochecotte, which belonged to Boniface's mother.

On 3 April 1866, he married Madeleine Le Clerc de Juigné (1847–1934) in Paris.