After a frustrating time at the art academy between 1939 and 1940, Constant met the Danish artist Asger Jorn. They became friends and the dynamic, internationally oriented Jorn encouraged Constant to start a new avant-garde group in the Netherlands: the Experimental Group, which would later become Cobra. Constant not only played in Holland an important artistic role within Cobra, but also a theoretical one.
Art historian Willemijn Stokvis in 2017: Constant was the catalyst of Cobra, because he was so Marxist at the time. That Marxism forced the group together.