Christensen was a graduate of the Minneapolis College of Art and Design in Minneapolis. After finishing school he worked for the Walt Disney Studio from 1937 to 1941. He left the studio after the 1941 Disney animators' strike, during which he met his wife-to-be, Ivy-Carol Van Horn, a special effects detail artist. Christensen then worked briefly at Warner Bros. studio, primarily as a storyboard artist for Bob Clampett's animation unit. After leaving Warner Bros. he worked independently for nearly four decades as a storyboard writer and artist, primarily for Western Publishing, Dell and Gold Key comic books, as well as Hanna Barbera, Walter Lantz Productions, DePatie-Freleng Enterprises, and other cartoon studios. He wrote and provided illustrations for such comic book titles as "Magnus, Robot Fighter," "Donald Duck," and "Uncle Scrooge". He was involved with the Southern California Comic Artist Professionals Society for many years, and was a past President of the Comic Art Professional Society (CAPS).