Karen-Marie Flagstad (November 24, 1904 – December 25, 1992) was a Norwegian soprano opera singer. Flagstad was born in Oslo and was one of Norway's leading singers in her time. She was the sister of the world-renowned singer Kirsten Flagstad, and the daughter of the conductor Michael Flagstad and the pianist Maja Flagstad. Flagstad was employed at the Norwegian National Opera and Ballet (led by her sister) from 1958 to 1961, where she was acclaimed in the role of Ågot in Waldemar Thrane's Fjeldeventyret (The Mountain Tale, 1960) and later worked as a répétiteur (like her mother).