Together with Karel Appel and Constant, Corneille was one of the founding members of CoBrA. Rejecting rational Western culture as well as its rules and conventions concerning art, the international movement of Danish, Belgian and Dutch artists aimed to provoke while referring to forms of expression like primitive art, prehistoric art, art from the Middle Ages, children's drawings and art of the mentally handicapped. Corneille was an active member of the group, not only as a productive painter, but also as a poet for CoBrA magazine.

Following the footsteps of his idol Paul Klee, Corneille started his first journeys to North Africa in 1948. In Tunesia and later during a journey to the Hoggar mountains in South Algeria (Sahara) he was impressed by the intensity and multiplicity of colours, the deserted landscapes and the austere expression of the masks and statues he saw. He discovered an entirely different, colourful, authentic and primitive African culture. These impressions were to become of lasting influence on many of his works. The journeys to Africa not only had a balancing effect on his figurative style but also the content and choice of subject matter became calmer and reflected on.

Corneille would never lose his fascination for Africa, its people, its nature, its culture and its art. After CoBrA dissolved in 1951, Corneille moved to Paris and became a passionate collector of African art. The primitive artefacts played an prominent role in his paintings, which then began to take on a more imaginative style, with bird's eye view landscapes, exotic birds, nudes and stylised forms.