Stein was born in New York from Jewish parents, and from an early age took an interest in science. He earned degrees in psychology and zoology, a doctorate in physiology from Ohio State University and masters degrees in Management and Library Science from University of Rochester, Adelphi College, and the University of California at Los Angeles.
He was an author of books for secular humanist and rationalist publications, he also was a critic of claims of paranormal phenomena. Stein was an outspoken atheist and publicly debated Christian apologetics such as Greg Bahnsen. He served as editor of the American Rationalist and was the librarian of the Center for Inquiry, which houses both the Committee for the Scientific Investigation of Claims of the Paranormal (CSICOP) and the Council for Secular Humanism (CSH).
Stein died of cancer in Buffalo General Hospital. He was survived by his first wife, Barbara, and a daughter, Karen, both of Atlanta. He was also survived by a second wife, Eve Triffo of Los Angeles, California, and a sister, Irna S. Jay of Baltimore.
He published articles critical of the paranormal in the Skeptical Inquirer. His book The Sorcerer of Kings: The Case of Daniel Dunglas Home and William Crookes (1993) is a debunking of the mediumship of Daniel Douglas Home. He also edited the Encyclopedia of the Paranormal (1996) which received positive reviews. Stein had exposed a number of fraud mediums. He discovered a levitation photograph of Carmine Mirabelli had been chemically retouched.
- Robert Ingersoll: A Checklist (1969)
- Free thought in the United States: A Descriptive Bibliography (1978)
- Anthology of Atheism and Rationalism (Editor, with Marshall Brown (1980)
- Freethought in the United Kingdom and the Commonwealth: A Descriptive Bibliography (1981)
- Encyclopedia of Unbelief (Editor, 1985)
- A Second Anthology of Atheism and Rationalism (Editor, 1987)
- God Pro and Con: A Bibliography of Atheism (Editor, 1990)
- The Sorcerer of Kings: The Case of Daniel Dunglas Home and William Crookes (1993)
- Encyclopedia of Hoaxes (Editor, 1993)
- Encyclopedia of the Paranormal (Editor, 1996)