Claude Auclair took courses in Fine Arts in Nantes. Afterwards, he became a theatre decorator. He got involved with comics through Robert Roquemartine, the founder of Futuropolis. In the late 1960s, he began illustrating science-fiction periodicals. He was pushed by his fellow artists Moebius and Philippe Druillet to join Pilote magazine in 1970. There, he drew several short stories, and later the 'Jason Muller' series. When editor-in-chief René Goscinny cancelled the series, Auclair moved over to Record, where he began drawing the 'Catriona McKilligan' series (text by Jacques Acar).
Auclair began his most famous series, 'Simon du Fleuve', in Tintin, doing both text and artwork. This post-apocalyptic saga ran until 1978 and had a brief reappearance in 1988, when Auclair took on a second cycle until 1989. Claude Auclair joined the team of À Suivre in 1978. For this magazine, he began producing humanistic stories about Negro slavery ('Le Sang Flamboyant') and Breton history ('Bran Ruz'). While working on the final part of his 'Celui-là' trilogy, Auclair prematurely passed away in 1990, leaving the book to be finished by his friends Mézières and Tardi.