As a poet he enjoyed the rare honor of being mentioned in glowing terms—along with French contemporaries Charles Baudelaire, Gustave Flaubert, Stéphane Mallarmé, Tristan Corbière, and Paul Verlaine—by Des Esseintes in Joris-Karl Huysmans' famous decadent novel, À rebours[2] Born October 1, 1851, at Ixelles, Belgium, and died April 7, 1916, at Etterbeek, Belgium, Théodore was the second of three siblings.

His father, Joseph-Désiré Hannon [fr] (1822-1870), was a doctor of medicine and a professor of natural sciences (botany, zoology) at the Free University of Brussels.

[3] Hammond first followed in the footsteps of his deceased father, by enrolling in a study of the sciences (1870-1871) and then medicine (1871-1873) at the Free University of Brussels.

In the November 26, 1876, issue of The Artist, Hannon dedicated an article of high praise to Martha, which Huysmans thanked him for in a long letter dated December 16, 1876.

Huysmans later repaid the favor (of Hannon's positive review) publicly by writing the preface to a subsequent book of Hannon's poetry, Rhymes of Joy (Rimes de joie), but also—much more importantly—by including praise for the Belgian poet in the mouth of his character Des Esseintes, in Huysmans' seminal decadent novel À Rebours:[2] "[speaking of Tristan Corbière's] decadence... des Esseintes discovered it again in another poet, Théodore Hannon, a disciple of Baudelaire and Gautier, ripe in the special sense of studied elegances and factitious joys...."[2]