Krohg's work as an artist covered a wide field, from paper drawings, illustrations, and posters to set design, sculpture, and monumental paintings. After returning to Norway in 1930 he taught at the National College of Art and Design in Oslo. During the Second World War, he was a forced laborer at the Veidal Prison Camp. In 1946 he was appointed professor at the National Art Academy, and served as its director from 1955 to 1958. Among others, his students included artists Frithjof Tidemand-Johannessen and Tulla Blomberg Ranslet.