Margarete "Grete" Steffin was born to a working-class family in Rummelsburg, now part of Berlin, Germany. She began writing at a young age and one of her verse-dramas was performed in three different schools. At age 14, she left school at her father's request, though she continued her education on her own through evening courses, lectures, and reading. She took a job with the phone company and then with a publishing company. Her interest in leftist politics led her to learn Russian and participate in the Rote (Red) Revue. In 1931, she took a speech class from Helene Weigel, actress and wife of Bertolt Brecht. She met Brecht that year through her involvement with the Theater am Schiffbauerdamm, and became his secretary and then his lover.
In 1933, Brecht and Weigel went into exile in Denmark to escape the rise of Nazism. Margarete made an arranged marriage to a Danish citizen in order to continue working with Brecht and followed the couple to Finland and Russia when World War II broke out. Brecht named her as his collaborator on his plays Roundheads and Peakheads, Señora Carrar's Rifles, and The Horatians and the Curiatians. He also acknowledged her role in the creation of Fear and Misery in the Third Reich, Life of Galileo, and Mother Courage. She died in Moscow at age 33 in 1941 while awaiting a visa for travel to the USA.