Appel studied at the Royal Academy of Beaux-Arts in Amsterdam.
He was a leading light in the CoBrA* group. He moved to Paris in 1950 but in 1957 took up permanent residence in New York. He is a prolific painter and printmaker. The intensely colourful expressionist lithographs he made with L'Ouevre Gravée were the highlights of his graphic work and are much prized by collectors.

*CoBrA - (Copenhagen, Brussels, Amsterdam) the group of abstract artists originally started by Asger Jörn, Corneille and Appel in 1948.

Right: photograph of Appel by Ida Kar, late 1950s