Käthe Loewenthal was born in Berlin, the eldest of five daughters. Her father’s scientific work meant that Käthe’s family travelled often. The Loewenthals were Jewish, but Käthe had herself baptised and confirmed when they lived in Bern between 1892 and 1894. Loewenthal’s interest in art began at an early age. After finishing school, she studied under Ferdinand Hodler until 1897. She made several study trips, on some of which she was joined by her sister Susanne Ritscher. She then moved to Berlin, where from 1903 to 1904 she attended the private painting school run by Leo von König. At this time, she began a close friendship and romantic relationship with the painter Erna Raabe, Countess von Holzhausen.
In 1905, Loewenthal began to work as a freelance artist in Munich. She became a member of the Association of Lady Artists in Munich, and attended courses run by the “Ladies’ Academy” of the Association. Her still life Green Apples was painted at this time, in ca 1905/06, and is one of her few extant oil paintings. In 1909/1910, she moved into a studio in the house of the Württemberg Association of Lady Painters in Stuttgart. In 1910, she attended the ladies’ painting school run by Adolf Hölzel at the Academy of Fine Arts. From 1912 onwards, she spent her summer months at Hiddensee, where she painted seascapes and landscapes. She moved to Stuttgart in 1914 as a freelance artist and participated regularly in exhibitions, including those of the Stuttgart Secession.
Her Jewish background meant that Loewenthal was forbidden from painting in 1934; this was followed by the termination of the lease for her studio and her exclusion from the Württemberg Association of Lady Painters. She was not allowed to participate in exhibitions, nor to sell her paintings. In 1939, she was moved to a “Jewish apartment” in Stuttgart-Kaltental and in February 1942 she was deported to the transit camp of Izbica near Lublin in occupied Poland, where she was murdered. Many of her works were in storage in Stuttgart, and were destroyed in a bombing raid in 1943; a large number of them were paintings.