Margit Simonsen was born in Frederiksberg and grew up with her father, the author and mystic J. Anker Larsen, after her parents' divorce in 1918. She passed the upper secondary school leaving examination, worked in an office, and then became a housewife. From the 1950s, during long stays in Greece, she became involved in the resistance movement against the military junta. She started attending university in 1968, became a Redstocking and a member of Socialistisk Kulturfront (socialist cultural front), was married, and had two children.
In her diary novels, she fights against the weakness of the self and external despotism, quite subtly in her debut work Sort og hvidt, 1946, but later more flagrantly in her semi-documentary, artistically fully developed work De ansigtsløse, 1973, which manifests a modern, liberated point of view.