Sébastien Cosset studied architecture at the Academy of Applied Arts. He began the series 'Res Punica', which was scripted by his father Jean-Marc Cosset, at Glénat in 2001. In 2003 he drew the fifth episode of 'Rogon Le Leu', a series that was previously drawn by Alexis Chabert (text by Didier Convard).
Together with Marie Pommepuy he forms the art duo Kerascoët. Under this pen name, they have drawn series like 'Donjon Crépuscule', 'Miss Pas Touche' and 'Jolies Ténèbres'.