Singer was born on November 21, 1902 in Leoncin, Poland. His father was a Hasidic rabbi and his mother, Bathsheba, was the daughter of the rabbi of Biłgoraj. Both his older siblings, sister Esther Kreitman (1891-1954) and brother Israel Joshua Singer (1893-1944), became writers as well. Esther was the first of the family to write stories.
The family moved to the court of the Rabbi of Radzymin in 1907, where his father became head of the Yeshiva. After the Yeshiva building burned down in 1908, the family moved to a flat at ul. Krochmalna 10. In the spring of 1914, the Singers moved to No. 12. The street where Singer grew up was located in the impoverished, Yiddish-speaking Jewish quarter of Warsaw. There his father served as a rabbi, and was called on to be a judge, arbitrator, religious authority and spiritual leader in the Jewish community.