He was born in 1859 in Weisskirchen, Moravia, in the Austrian Empire (today, Hranice/Přerov District, Czech Republic). Singer studied at the Universities of Vienna and Berlin, receiving his Ph.D. in 1884. After editing the Allgemeine oesterreichische Literaturzeitung [Austrian literary newspaper] from 1885 to 1886, he became literary secretary to the French ambassador in Vienna. From 1887, he worked in Paris in the press bureau of the French foreign office and was active in the campaign on behalf of Alfred Dreyfus.
Singer moved to New York City in 1895 where he raised the money for the Jewish Encyclopedia he had envisioned and subsequently edited the twelve-volume work (1901–1906) himself.