Born in Paris, the son of the architect Achille Hermant (1823-1903), Hermant was educated at the École des Beaux-Arts under Joseph Auguste Émile Vaudremer. He was a rationalist architect, but was a strong advocate for the neoromanticism style of the time, preferably the style of Louis XIII. Hermant became an advocate for concrete construction and erected two of the first reinforced concrete buildings in Paris, collaborating with the French engineer Edmond Coignet (1856–1915), who patented his system in 1892.
- the French pavilion for the World's Columbian Exposition, Chicago, 1893
- the French pavilion for the Exposition Internationale, Brussels, 1897
- La Caserne des Célestins, Paris, 1895–1901. Home of the cavalry of the French Republican Guard.
- Le Magasin des Classes Laborieuses, department store, reinforced concrete (with Coignet), Paris, 1899
- La Salle Gaveau, concert hall for the piano firm, reinforced concrete (with Coignet), Paris, 1905
- Société Générale, office building, Blvd. Haussmann, Paris, 1907
- Balteau, J. (editor), Dictionnaire de biographie française, 1933.
- 'Livraisons d'histoire de l'architecture, 2003, Vol. 6, Number 1, p. 47–67.