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. In 1893 he founded a short-lived biweekly called La Vraie Parole as a foil to the anti-Jewish La Libre Parole.
Over the course of his career, Singer also proposed many projects which never won backing, including a multi-million-dollar loan to aid the Jews of Eastern Europe, a Jewish university open to students of any background, various encyclopedias about secular topics, and a 25-volume publication series of Hebrew classics. By 1911, the date of this latter proposal, "neither the [Jewish] Publication Society nor any body of respectable scholars would work with him," according to encyclopedist Cyrus Adler.
Singer held extremely liberal views which at times proved unpopular. He endorsed Jesus and the Christian New Testament and proposed a Hebrew translation. He founded the Amos Society to promote understanding among followers of monotheistic religions.
His 1897 prospectus for the encyclopedia project called for harmony between religions; called the Sabbath and holidays "heavy burdens, or, at best, mere ceremonies" for most Jews; and made the radical suggestion that Jewish parents, if honest with their children, would tell them:
"Our religion ... does not accord with your ideas. We have neither the power nor the desire to impose it on you. Make your peace with your God and your conscience as best you can," and, that said, let us cease to erect new synagogues, let us close our seminaries of theology, and let us disintegrate, little by little, our ancient communal institutions.
Due to the controversy of Singer's outlooks, his publisher, Funk & Wagnalls, agreed to the encyclopedia project only after divesting Singer of editorial control and appointing a board of prestigious Jewish scholars, including rabbis.
- The Jewish Encyclopedia Funk & Wagnalls, 1901–1906.
- Russia at the Bar of the American People: A Memoir of Kinship. Funk & Wagnalls, 1904. (PDF, Internet Archive)
- The German Classics (c. 1913–1914), with Kuno Francke: twenty volumes. (Search results at Internet Archive.)
- A Religion of Truth, Justice, and Peace: A Challenge to Church and Synagogue to Lead in the Realization of the Social and Peace Gospel of the Hebrew Prophets. Amos Society: 1924. (PDF)
- "Biographical Sketch". Finding Aid to the Isidore Singer Papers. American Jewish Archives. Retrieved 2016-11-01.
- Temkin, Sefton (2007). "Isidore Singer". Encyclopaedia Judaica. 2nd ed. Macmillan Reference USA. Retrieved via Biography in Context database, 2016-11-01.
- Schwartz 1991, p. 20. "It folded in less than a year, however, partly because of the mood and priorities of the French Jewish community at that time, a majority of whom did not support a direct, vocal response to antisemitism. Yet, part of the failure can be attributed to Singer himself: the historian Michael Marrus has called him a 'latter-day Amos'; he castigated the wealthy Jews of France for their lack of support for Jewish causes in general and his journal in particular. Such personal attacks coupled with Singer's general assaults on the French social system, coming as they did from a foreigner, served to alienate him from the very Jews he wished to represent. It is not surprising that he left for New York the following year."
- Schwartz 1991, p. 20.
- Schwartz 1991, pp. 21–22.
- Schwartz 1991, p. 29.