Edgard Gastmans studied at the art academy in Antwerp from the late 1950s. After some commercial design work, he debuted at the 'Bessy' department of Studio Vandersteen under Karel Verschuere in 1967. When Verschuere departed, Gastmans and Frank Sels assumed control over the 'Bessy' production. But after only a year, Gastmans joined Sels in the creation of Studio Sels, in order to produce 'Silberpfeil' for the German market.
Gastmans didn't stay long at the Sels studio, and then went back to drawing advertisements again. At the start of the seventies, he collaborated with Jef Nys on the series 'Jommeke', among other projects. Gastmans later started the series 'Willeke', which ran for six albums. For this series, which was largely based on 'Jommeke', Gastmans was eventually condemned because of plagiarism.