He began working with famed Belgian cartoonist Jijé, first on his ambitious New Testament comic project Emmanuel.
He then succeeded Jijé as illustrator of the detective series Valhardi, published in the Franco-Belgian comics magazine Spirou.
Paape illustrated the series from 1946 until 1954, working with famous European comics authors Jean-Michel Charlier and Yvan Delporte.
Paape's best-known collaboration began in 1966, when he created the Flash Gordon-like science fiction series Luc Orient with Greg.
In 1969 Paape began teaching draughtsmanship for comics at the Institut Saint-Luc art school in Brussels, where he remained until 1976.