He was born in 1859 in Weisskirchen, Moravia, in the Austrian Empire (today, Hranice/P?erov 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.