In Vienna, she met the psychiatrist and psychoanalyst Kurt Robert Eissler (1908–1999), co-founder of the Sigmund Freud Archives, and they married in 1936. After Austria was annexed to Germany by Hitler on March 12, 1938 (an event known as the Anschluss) the couple moved to the United States arriving in Chicago, where she joined the Chicago Psychoanalytic Society while working as a child psychiatrist at the Michael Reese Hospital. During the Second World War, Ruth Eissler was a consulting physician in a program for young delinquent women in Chicago and in 1949 published a paper about her work.