Geyer joined the Bavarian State Police in 1927 and transferred to the Munich Police Department in 1934. In October 1939, he was transferred to the Augsburg criminal police office and shortly afterwards promoted to criminal chief assistant. In January 1941, Geyer joined the police administration in Bromberg, where he remained until the end of the war, holding the rank of detective secretary starting in 1944. Geyer had joined the SS in 1940 and held the rank of head squad leader.
Geyer remained in British captivity until April 1946. In December 1946, he returned to the police service and became a case officer in the intelligence department of the newly established Central Office for Criminal Identification, Police Statistics, and Police Intelligence, the predecessor of the Bavarian State Criminal Police Office. In February 1950, Geyer was appointed head of the 'Information Collection and Inquiry Office on Vagrants', a field in which, according to his superior, he had many years of experience. He also knew how to deal smoothly with the "often difficult to handle group of vagrants". He regularly appeared as an expert witness in restitution proceedings for people formerly persecuted as 'gypsies'. After internal disputes, during which his former SS membership, which had been undisclosed at the time of hiring, was brought to light, he was assigned different tasks in 1957. Promoted twice more, Geyer retired in 1969 as a chief inspector.
