Knauer grew up in the Sasel quarter of the borough of Wandsbek with her younger brother, Tim.

She joined a child modelling agency after being spoken to in the Alstertal-Einkaufszentrum, a shopping centre, when she was 15.

[1][2] After completing her abitur in Hamburg, Knauer studied film and literature at the Free University of Berlin.

In 1996, when she was 17, Knauer gained her first role in Martin Gies's ZDF television film Kleine Einbrecher.

[1] The film Küss mich, Frosch, in which Knauer was the leading actress and played alongside Matthias Schweighöfer, won an Emil, a Goldener Spatz and an Erich Kästner-Fernsehpreis (for the screenplay),[3] and was nominated for an Emmy Award.