Käthe Schmidt was born in the industrial seaport of Königsberg, in the German annexed territories known as East Prussia, where her father was a member of the officially disapproved Social Democratic Party, and her maternal grandfather was a preacher in the radical Latitudinarian Community he founded there.

After art studies there, and further in Berlin and Munich, in 1890 Käthe married with Karl Kollwitz, a former medical student of her home-town, who after graduation had set up as a member of a subscription medical practice in the poorest part of Berlin. Here they spent the best part of their lives, in Käthe's case including the entire Nazi era-until driven out by the large-scale bombing of the city.