Melanie Steinmetz graduated as a teacher in Hamburg in 1933, then worked in a bookstore in Stettin. In 1937 she moved to Berlin, where she worked for the publishing houses Rembrandt-Verlag and later Propyläen Verlag.
In Berlin, Melanie Steinmetz regularly attended services at the Dahlem confessional community. She joined the Confessional Church in 1938. In Dahlem, she came into contact with the helpers grouped around Franz Kaufmann. Gertrud Staewen put her in touch with persecuted Jews, for whom she collected food and money. Steinmetz and Helene Jacobs also looked after a Jewish boy.
Melanie Steinmetz was arrested on August 21, 1943, and sentenced to a year and a half in prison. During her time in various Berlin prisons, she took on housekeeping tasks and performed medical assistance. Her appeal for clemency was granted on October 17, 1944. She was released on the condition of serving in an armaments company important for the war.
In 1984, Melanie Steinmetz was to be honored with the Federal Cross of Merit. She refused to accept, since she rejected any official honors for her help.