Johanna Sedule lived with her husband, the janitor Robert Seduls, and their daughters Indra and Irīda in Liepāja. In July 1941 German troops occupied the Latvian city, using violence against the Jewish population. Johanna Sedule and her husband Robert were horrified by the anti-Jewish measures. Robert Seduls promised his Jewish friend David Zivcon, who had to move into the ghetto, to help him in an emergency.
In October 1943 David Zivcon escaped from the Liepāja ghetto with his wife and another couple. Johanna and Robert Seduls took the escapees in and hid them in the basement of the building where they were tenants. They took in more people at risk over the next few months. A total of eleven Jews lived in the basement for 19 months. It was difficult for the Seduls family to provide them all with food, and they were under constant threat of discovery.
When Robert Seduls was killed by shrapnel in March 1945, Johanna Sedule continued to look after the people in hiding, along with Arvīd Skara and Tonija Pļūkše, until their liberation a month later.
Johanna Sedule was honored as Righteous Among the Nations in 1981.