After studying art in at the Saint-Luc in his native town Roubaix, François Dermaut was employed by the publisher Fleurus in 1974. Using the pseudonym Franjack, he made his debut with a comic adaptation of 'Oliver Twist', which appeared in the magazine Djin. He subsequently adapted 'Les Misérables' and 'Jacquou le Croquant' for this magazine, and made several short historical comics. Until 1978, he also cooperated with the magazines Fripounet and Triolo.
His first album, 'Jacques Laval', was published in the collection Les Grandes Heures des Chrétiens by Univers-Média in 1978. During the eighties, he teamed up with Daniel Bardet, with whom he created the prestigious historical series 'Les Chemins de Malefosse', which he signed with his own name, in 1982. The series was published in the magazines Circus and Vécu, and later on in albums by Glénat. While working on this saga, he made 'Charlotte et le Secret des Tempeliers' in Okapi in 1985.
In 1989, with Didier Convard, he launched 'Souvenirs de Toussaint', a series of which he drew the first three episodes, before handing over the graphical duties to Joëlle Savey in 1996. After a period of inactivity due to personal problems, he returned to the field with 'Carnets de Saint-Jacques de Compostelle', an illustrated book published by Glénat in 2003.