Christiaan Karel Appel was born on 25 April 1921 in his parents' house at Dapperstraat 7 in Amsterdam, Netherlands. On the ground floor, his father, Jan Appel, had a barber shop. His mother, born Johanna Chevalier, was a descendant of French Huguenots. Karel Appel had three brothers.
At fourteen, Appel produced his first real painting, on canvas, a still life of a fruit basket. For his fifteenth birthday, his wealthy uncle Karel Chevalier gave him a paint set and an easel. An avid amateur painter himself, Chevalier gave his namesake some lessons in painting.
He studied at the Rijksakademie van Beeldende Kunsten from 1940 to 1943 and had his first show in Groningen in 1946. He was influenced by Pablo Picasso, Henri Matisse and Jean Dubuffet; he joined the Nederlandse Experimentele Groep and joined CoBrA in 1948 together with Corneille, Constant and Jan Nieuwenhuys. His 1949 fresco 'Questioning Children' in the Amsterdam City Hall caused controversy and was covered up for ten years.
As a result of this controversy Appel moved to Paris in 1950 and he developed his international reputation travelling to Mexico, the USA, Yugoslavia and Brazil. He is particularly noted for his mural work and lived between New York and Florence.
Appel died on 3 May 2006 in his home in Zürich, Switzerland. He suffered from a heart ailment.