Olivier Grenson knew he wanted to become a comics artist since he was ten years old. He learned the finer points of the profession from Vittorio Leonardo, taking courses at the Academy of Châtelet. He subsequently studied at the School of Graphic Research in Brussels, focusing on animation. In the evenings, he worked with Eddy Paape, who introduced him to the publishing house Lombard in 1984. In 1984-85, he drew the humorous series 'Aldose et Glucose' in the publisher's magazine Tintin. A few years later, he made his first realistic comics with scripts by the Rahir sisters for the same magazine.
In addition, Grenson worked on some television projects with Patrick Chaboud for RTBF. Also with Chaboud, he made the shortlived series 'Jack et Lola' in Circus in 1989. That same year, he joined the publishing house Claude Lefrancq and began working on the fantasy detective series 'Cartland Cross' with writer Michel Oleffe. The series, that appeared in albums from 1991, was also adapted into a series of cartoons by Kid Cartoons and broadcasted by Canal +. In 1999, Grenson teamed up with Jean Dufaux to start 'Niklos Koda' for the collection Troisème Vague of Lombard. In addition to his work on this series, he created 'La Femme Accident' with Denis Lapière for the Aire Libre collection of the publishing house Dupuis in 2008.