Kjell Nupen exhibited in several countries. Before the age of 20, his artwork was purchased by several important institutions. Nupen was an achieved painter that worked with diverse types of materials. Nupen was accepted into the Norwegian National Academy of Fine Arts at the age of 17, and two years later he debuted with paintings and graphics at The National Art Exhibition in Oslo.
Nupen also made several public commissions, but he is best known for designing the Otterdal Park in Kristiansand, a sculpture facility that opened in 1991. Also, Nupen is known for his collaboration with Her Royal Highness, Queen Sonja of Norway.