Her father was a retired Prussian Army captain, her mother, Helene (1837–1924), was an amateur artist and her younger sister, Elisabeth Siewert [de] became a popular novelist.

In 1884, she began to divide her time between Budda and Berlin and was finally able to secure lessons from a notable painter, the Swiss portraitist, Karl Stauffer-Bern, who introduced her to the work of the Symbolist, Arnold Böcklin; a major influence on her style.

In 1936, the gallery owner Wolfgang Gurlitt became aware of her and organized the largest exhibition of her works during her lifetime (174 pieces) but it was not a critical success.

For many years, it was believed that she was killed during a bombing raid in 1944, but a letter from her sister Victoria, published in 2012, indicates that she died shortly after the end of the war from a heart ailment.

She was largely forgotten until 2008, when a major retrospective was presented at the Kunstforum Ostdeutsche Galerie [de] in Regensburg, titled "Clara Siewert - Between Dream and Reality".