John Thomas Sladek was born in Waverly, Iowa on December 15, 1937. He attended the College of St. Thomas (later the University of St. Thomas) from 1955-1956 and graduated from the University of Minnesota in 1959. Before he became a professional author Sladek held a number of different jobs, including working as a engineering assistant at UM, a technical writer for Technical Publications, Inc. of St. Louis Park, MN, a switchman for the Great Northern Railway from 1962-1963, and as a draftsman in New York City from 1964-1965.

Sladek began writing short stories in the early 1960s while living in America, but he moved to Great Britain in 1966, where he lived and worked for the next 20 years. His first novel was The Castle and the Key(1966), a non-SF Gothic novel written under the pseudonym "Cassanda Knye". As a science fiction writer he quickly became identified as part of the "New Wave" SF literary movement (led by Michael Moorcock).

Sladek is particularly notable for the surreal, satirical and blackly humorous nature of his work. Sladek himself noted that his novels and stories "are set in the near future, in a recognizable America in which technology has either solved all of our problems or failed to solve any of them, or something else entirely is happening. Something else entirely is always happening in science fiction, I understand." Much of his work (such as his 1980 novel Roderick, or The Education of A Young Machine) is informed by the concept of machines that can mimic or even displace human beings. He is also concerned with the process of dehumanization - with the ways in which governments and other institutions, as Sladek puts it, "attempt to reduce their citizens or members to mechanical components." This theme resonates in our own society today, and thus provides Sladek's work with continuing relevance.

Sladek was a firm materialist, deeply skeptical of claims of the occult and supernatural. In 1973 he wrote The New Apocrypha: A Guide to Strange Science and Occult Beliefs, an expose of these types of beliefs. Under the pseudonym James Vogh he wrote Arachne Rising(1977), a supposed "true" account of a thirteenth sign of the zodiac suppressed by the scientific establishment, and The Cosmic Factor : Bioastrology and You.

He also produced two pseudonymous novels with his friend Thomas M. Disch: the Gothic thriller The House that Fear Built(1966; again as "Cassandra Knye") and the satirical thriller __ Black Alice(1968; as "Thom Demijohn"). Sladek was also noted for writing a number of parodies of his fellow science fiction authors, which he collected in the 1973 anthology The Steam-Driven Boy and Other Strangers.

John Sladek returned from England to Minneapolis, MN in 1986. He continued to write once back in the United States, where he died of pulmonary fibrosis on March 10, 2000. He was the recipient of the British Science Fiction Association Best Novel Award in 1983 for the novel Tik-Tok, a black comedy that tells the story of a robot who liberates himself from his behavorial limits (expressed by his "asimov circuits", named for Isaac Asimov's Three Laws of Robotics and which prevent robots from harming human beings) and commits numerous acts of murder and other crimes.