After being trained by her father, she became a pupil at the school of the Royal Danish Theatre where she made her debut on 4 February 1900 as Pernille in Ludvig Holberg's Gert Westphaler.

[3] With her father's assistance, she was able to return to the Royal Theatre in 1912 where she performed comic roles such as Tante Malle in Bjørnstjerne Bjørnson's Geografi og Kærlighed.

At the Frederiksberg Teater, she took the leading role in Gustav Wied's Hendes gamle Naade (1941) and played Julia Gibbs, a mother in Thornton Wilder's Our Town (1942).

In 1931, as Tosse-Grete in Hotel Paradis, she embarked on her career in sound films taking mainly fairly minor roles, frequently as a strong or bohemian women.

[3] Karen Poulsen was married three times, first to the actor Valdemar Lund in 1902, then to the journalist and athlete Bjørn Thalbitzer in 1919,[7] and finally to the banker Mogens la Cour Kruse in 1928.