Kaus left school at fourteen in order to become a painter. He did an apprenticeship as a painter, but at the same time attended the School of Arts and Crafts in Berlin-Charlottenburg. After completing his apprenticeship in 1908, Kaus became a fulltime student of Meinhard Jacoby’s at the School, and also worked as a freelance decorative painter. He was awarded a travelling scholarship by the School, and went to Paris with his friend and fellow student Hans Orlowski. Kaus returned to Germany when the First World War broke out. He was trained as a medical orderly with the Red Cross. In Ostend, Kaus served in the ambulance unit of the art historian Walter Kaesbach, who used his position to prevent his artist friends from being sent to serve directly at the front. Kaus became firm friends with Erich Heckel, who was also his role model as an artist. After the war, Kaus returned to Berlin and had his first exhibition in 1919 in the gallery of Ferdinand Moller, after which he exhibited in the galleries of Paul Cassirer und Karl Nierendorf.
In 1920, Kaus joined the Free Secession in Berlin and became acquainted with Karl Schmidt-Rottluff and Otto Muller, with whom he embarked on several joint exhibitions. In 1926, he began teaching at his former School of Arts and Crafts in Berlin-Charlottenburg. In 1929, he was awarded the Villa Romana Prize of the Association of German Artists.
In 1935, Kaus began teaching figurative painting at the United State Schools of Free and Applied Arts in Berlin. But he suffered more and more under the repressive measures of the National Socialists. From 1937 onwards, many of his paintings were removed from exhibitions and museums, and in 1938 he was forced to abandon teaching. He went into inner emigration and restricted himself to painting landscapes. In 1949, Kaus was made a professor at the Academy of Fine Arts in Berlin.