Christianesen began his career as a carpenter and went on to study sculpture and ceramics at the Royal Danish Academy of Fine Arts. He began working for Fog & Mørup in 1940 and soon began designing lamps.
His creations were often characterized by organic shapes and innovative materials, such as opalescent glass and chromed metal. Some of his best-known lamps include the "Kogle" table lamp (1955), which resembles a pine cone, and the "Gulvlampe" pendant lamp (1958), which has a teardrop shape.
Christianesen's work has won several awards and been exhibited in museums around the world, including the Museum of Modern Art in New York and the Victoria and Albert Museum in London. Today, his lamps are highly sought-after by Danish design collectors and are considered emblematic examples of mid-century Scandinavian design.