Thierry Ségur moved to Paris at a very young age, where he studied applied arts at the École Duperré. In 1986, he began a fruitful collaboration with Casus Belli, France’s leading role-playing magazine, which was then booming thanks to the craze for Dungeons & Dragons and the world of fantasy. There, alongside Bruno Chevalier, he created the humorous character Kroc le Bô. This collaboration naturally led him to Delcourt, then a fledgling publishing house on the hunt for new talent in the style of French heroic fantasy. In November 1987, La Saison des Cendres (The Season of Ashes) was published—the first volume of his flagship series, Légendes des Contrées Oubliées (Legends of the Forgotten Realms)—which was an immediate success. The second volume, Le Pays des Songes (The Land of Dreams, 1989), propelled sales to over 45,000 copies—a remarkable achievement for the genre in France at that time. Le Sang des Rois (The Blood of Kings, 1992), the third and final volume, marked his breakthrough: the album topped the VSD/FNAC bestseller list for an entire month.
At the same time, Ségur spent over a year working on the storyboard for Trooper, a film by director Christophe Gans, before publishing Kroc le Bô (Kroc the Beautiful) as an album with Delcourt in 1990. After a five-year hiatus from comics, during which he focused on advertising and illustration, he returned in 1997 with an ambitious one-shot co-written with Igor Szalewa, Le Roi des Méduses (The King of the Jellyfish), adapted from a short story by Pierre Bettencourt. He also illustrated the adaptation of Hans the Pied Piper for the television series Il était une fois... (1995) and concluded his career in comic art with L’Encyclomerveille d’un tueur (A Killer's Encylowonder) published by Delcourt (2009–2011).