Friedrich Tillmann was born the son of a master blacksmith in Mülheim an der Ruhr in 1903 . After gaining his intermediate school certificate, he completed a commercial apprenticeship. In the 1920s, Tillmann, who had been raised as a Catholic, got involved in the youth movement and was temporarily a member of the NSDAP. As a member of an amateur dramatics group, he met Viktor Brack, who later became an organizer of the National Socialist murder of patients in the Chancellery of the Führer. In 1933, Tillmann joined the NSDAP again and rose in ranks of the Cologne city administration to head the entire welfare orphanage care. Brack recruited him in 1940 to ensure the smooth processing of the murder of patients. As head of the office department, the special registry offices set up to falsify death certificates were subordinate to him. At the same time, he continued to manage the Cologne orphanage care.
In August 1941, Tillmann retired from the service of the T4 and, until the war ended, organized several aid measures for the children entrusted to him.
After 1945, he was dismissed as the director of the Cologne orphanage care because of his support of the National Socialist regime. The criminal proceedings initiated against him for complicity in murder in 1960 were discontinued after his death from defenestration in 1964.