Influenced in racial hygiene and Social Darwinism by his brother-in-law Alfred Ploetz, Rüdin started his career as a psychiatrist and developed the concept of "empirical genetic prognosis" of mental disorders. He published his initial results on the genetics of schizophrenia in 1916.
Rüdin was the director (1917-1945) of the Genealogical-Demographic Department at the German Research Institute of Psychiatry.
Ernst Rüdin was the director of the one of the first eugenics research institutes, known as the Kaiser Wilhelm Institute for Genealogy in Munich, Germany. He also headed the Max Planck Institute for Brain Research in Frankfurt and the German Society for Rassenhygiene (Race-hygiene) and was one of the first members of the organization who attempted to "educate" the public on the "dangers" of hereditary defectives and the value of the Nordic race as "culture creators."
His research was later supported with manpower and financial funding from the National Socialist Party. After 1945, Rüdins connections to the Nazis were the main reason for criticism of psychiatric genocide in Germany.
Additionally Ruedin was president of the International Federation of Eugenic Organizations and world leader of the eugenics movement which sought to remove “inferior” individuals from society by segregation, sterilization, or death in order to create a “better” race.".
Recognized as one of the fathers of Nazi ideology, his work was endorsed officially by the Nazi Party. He wrote the official commentary for the racial policy of Nazi Germany: "Law for the Prevention of Hereditarily Diseased Offspring"; and was awarded medals from the Nazis and Adolf Hitler personally.
In 1933, Ernst Rüdin, Alfred Ploetz, and several other experts on racial hygiene were brought together to form the Expert Committee on Questions of Population and Racial Policy under Reich Interior Minister Wilhelm Frick. The committee's ideas were used as a scientific basis to justify the racial policy of Nazi Germany. The "Law for the Prevention of Genetically Diseased Offspring" was passed by the German government on January 1, 1934.
"The significance of Rassenhygiene did not become evident to all aware Germans until the political activity of Adolf Hitler and only through his work has our 30 year long dream of translating Rassenhygiene into action finally become a reality." - Ernst Rüdin.
"Whoever is not physically or mentally fit must not pass on his defects to his children. The state must take care that only the fit produce children. Conversely, it must be regarded as reprehensible to withhold healthy children from the state." - Ernst Rüdin at a speech to the German Society for Rassenhygiene, quoting Hitler.