Gerard Leever already knew he wanted to become a comics artist, when he was nine years old. He worked in a comic shop in Bussum (Wammes), where he met the legendary Flip Fermin (the brother of the owner), who gave him his first lessons in drawing comics. His first comic during this period was 'Superhobo', a character scripted by Fermin that later reappeared in the "Pincet" series. After school, he went into the army, where he kept a drawn diary - a first version of his famous 'Gleever's Dagboek'.
Leever continued this series of autobiographical strips in the comics information magazines Striprofiel and Stripschrift from 1980. In 1981, he was employed by comic magazine Eppo to draw the puzzles page. A year later, he joined the comic group Studio Arnhem. With fellow studio members Hanco Kolk and René Meulenbroek, he created 'Ernst Vrolijk en Dik Hout' for the magazine Robbedoes. For the same magazine, he also produced the gag strip 'De Vloek van Bangebroek'.
In the mid-1980s, he made 'Kanaal 13' for Eppo Wordt Vervolgd with writer Jan van Die, and he became the illustrator of the jokes section in Donald Duck weekly. In 1985, he began his famous series 'Oktoknopie' in Taptoe, a comic series that earned him the award for best Dutch children's comic book of the year 2000. Between 1990 and 1994, he drew 'Het Felix Flux Museum' in Sjors en Sjimmie Stripblad, a series co-scripted by Kees de Boer. When the series was cancelled, Gleever went to Suske en Wiske Stripblad to draw 'Dik van Dieren en Zo'.
In 1996, he started the family strip 'Gemengd Dubbel' in Tros Kompas, again in cooperation with Jan van Die. In 2001, he created the gag strip 'Suus & Sas' in girls' magazine Tina. Over time, he has produced many different comics, but his most impressive work is still his own comics diary, 'Gleever's Dagboek', for which he received the Stripschapspenning in 1996.
In 2006, he won the Stripschapprijs, the most important Dutch award for comic artists. In that same year, he created 'Ria en Rinus', a strip for the 50+ magazine Camé, with Patty Klein. In 2008-09 he made new stories of 'De Vloek van Bangebroek' for Jetix Magazine. Gleever has additionally drawn 'Ben Benieuwd' in NOS Jeugdjournaal Magazine, 'Pim, Pam en Pluis' in Roetsj (since 2007) and 'De Yeti's' in Dolfje Weerwolfje.