A sculptor and painter, Appel was born in Amsterdam, Holland in 1921. He attended the Rijksakademie van Beeldende in Amsterdam where he studied from 1940-1943. His first solo show was at Het Beerenhuis in Groningen, the Netherlands. He was influenced somewhat by Picasso and Matisse.
Appel moved to Paris in 1950 and here his works were exhibited extensively. He was given a solo show in 1953 at the Palais des Beaux-Arts in Brussels and in 1954 received the UNESCO prize at the Venice Biennial. During the 1950s and 60s, he produced countless murals for public buildings, including a mural for the restaurant of the Stedelijk Museum in 1956. In 1972 a retrospective of his work toured the U.S. and Cananda.