Benjamin Międzyrzecki and his three siblings lived with their parents in Warsaw. After the German invasion in 1939, the Międzyrzeckis were subjected to persecution as Jews. The area where the family lived was declared a ghetto in 1940.
In 1942 more and more ghetto inmates were deported to extermination camps. Międzyrzecki arranged his family’s escape from the ghetto and found refuge for them with a non-Jewish acquaintance, Julianna Larysz. When that hiding place was no longer safe, he organized a new one in a shed in an Orthodox cemetery in Warsaw.
He himself lived under a non-Jewish false identity, with forged papers. The Jewish combat organization ŻOB spent 1943 preparing an armed uprising in the ghetto. Międzyrzecki set up hiding places for fighters escaped from the ghetto. In the course of this work, he met a woman he had previously helped escape the ghetto in 1942, Feigele Peltel. The two of them worked for the ŻOB until the Warsaw Uprising was put down in 1944. They then went into hiding near Warsaw until their liberation. Benjamin Międzyrzecki and Feigele Peltel married in early 1945.