After the National Socialists took power in 1933, Magill joined the SS and directed the riding instruction of an SS Reitersturms. In March 1935 he became a full-time SS leader riding instructor at the SS Junker School in Braunschweig and made a career there. At the end of 1935 he was promoted to SS-Hauptsturmführer and, after he joined the NSDAP in 1937 (membership number 4.137.171), to SS-Sturmbannführer on April 20, 1938.