Ruth Müller-Stein studied law at the Universities of Berlin and Bonn. After an extended stay in the USA, she passed the Second State Examination in Law in 1978 and was appointed judge in Cologne (Appointment for Judge for the Regional Court of Cologne) that same year.
She held this position until 1992. Then she came to Munich, where she joined the BUSSE law firm in the summer of 1992. She is currently a partner in the law firm.