At the 1936 Berlin Olympics Gisela Jacob-Arendt won two Olympic medals under her maiden name Arendt. She won the silver medal with Leni Lohmar, Inge Schmitz and Ruth Halbsguth in the 4x100m freestyle relay, and she won the individual bronze medal in the 100m freestyle. She was the only German swimmer from the 1936 Olympics to take part in her country’s next Olympics in 1952 and finished seventh with the 4x100m relay at Helsinki.
At the 1934 European Championships she finished second in both the 100m individual backstroke and 4x100 freestyle relay, and was third in the 100m freestyle. From 1933-37 she won the German 100m freestyle title five times in a row, and again in 1939 and 1949. She also won the 100m backstroke title in 1934. Arendt was the sister of Olympic swimmer Heinz Arendt and the mother of Rainer Jacob. After World War II Gisela, together with Leni Lohmar, coached youth swimmers at her home club SSF Bonn.