Kåge was a well-established graphic designer when he began working for Gustavsberg in 1917. Kåge had initially undertaken to study painting under Carl Wilhelmsson in Gothenburg and later with Johan Rohde in Copenhagen. He studied graphic techniques at the Plakatschule in Munich and was also a pupil of Henri Matisse in Paris. At Gustavsberg, Kåge was quickly appointed artistic director, and designed many of Gustavsberg's advertising campaigns.The breadth of Kåge's experience as a painter and graphic artist translated into his pottery, which often took stylistic cues from modern painting and sculpture. Kåge's experience working across multiple media lead him to produce many extraordinary pieces. Kåge's works were showcased in major exhibitions across Europe and garnered positive critical acclaim. Káge was the recipient of several notable prizes including the Grand Prix in Paris for ceramics in 1925 and the Prince Eugen Medal for design in 1949.

Kage remained with Gustavsberg for 32 years, during which he designed 30 different dinner services. Most notable were his Praktika, Farsta, Surrea and Argenta lines. Kåge's Farsta line, which he conceived of in the 1920s, was an extremely successful series of unique stoneware vessels adorned with hand carved details and featured painterly applications of earth tone glazes.

Kåge remained at Gustavsberg until 1949, when he was succeeded by his pupil, Stig Lindberg. Kåge continued to create unique and artistic ceramic designs for the firm up until his death in 1960. Kåge's work is represented in prestigious collections such as the Museum of Modern Art in New York and The Metropolitan Museum of Art.