Oswald Rufeisen grew up in a Jewish family in Zadziele in southeastern Poland. Immediately after the German invasion of Poland in September 1939, the 17-year-old fled to Wilna (Vilnius, Lithuania). When the Wehrmacht invaded Lithuania in 1941, Rufeisen fled to Mir in Belarus. Since he spoke German without an accent, he posed as an ethnic German and worked as an interpreter for the German police in Mir. He maintained contact to local Jewish partisan groups.
When the approximately 300 Jews in the ghetto were to be murdered in August 1942, he warned them. Many ghetto inmates were able to escape because Rufeisen claimed a partisan assault was imminent, at which the guards hurried into the forests. More than a hundred escaped inmates were caught and murdered. Rufeisen was uncovered and was due for execution. He escaped and hid in a nearby convent, where he converted to Christianity. At the end of 1943, he joined a Soviet partisan unit.
After the war and his return to Poland, Rufeisen joined the Carmelite order. He was ordained as a priest in 1952 and performed pastoral work in Haifa (Israel) from 1959.