He published his first comics pages in the magazine Pilote in 1977. There, he created the series 'André le Corbeau', a series of fairytales in which animals are confronted with human problems, which was collected in three albums published by Dargaud ('Annie Mal', 'La Saison des Chaleurs', 'La Fuite en Avant').
He cooperated with Veyron on an illustrated children's book at Casterman ('Oncle Ernest et les Ravis'), and then made his first solo comic book at Futuropolis in 1978: 'Cours tout Nu'. In a more juvile register, he conceived the series 'Les Aventures de Rup Bonchemin' at Casterman between 1981 and 1983. Also present in À Suivre from 1979, he created the more adult series 'Luc Leroi' in 1980. After several shorter stories, this series soon made its claim to faim in longer albums, like 'Le Nain Jaune' (1985), 'Un Écran de Fumée' (1989), 'Bande d'Individus' (1998) and 'Toutes les Fleurs s'Appellent Tiaré' (2000).
In addition to 'Luc Leroi', Denis made 'Les Sept Péchés' ('The Seven Deadly Sins') in Métal Hurlant in 1982 (an album was published by Les Humanoïdes Associés the following year), and he cooperated on several collective projects. During a stay at the isle of La Réunion, he made 'Bonbon Piment' for Éditions du Bout du Monde.