Gardner, son of a petroleum geologist, grew up in and around Tulsa, Oklahoma. He attended the University of Chicago (UC) where he earned his bachelor's degree in philosophy in 1936. Early jobs included reporter on the Tulsa Tribune, writer at the UC Office of Press Relations and case worker in Chicago's Black Belt for the city's Relief Administration. During World War II, he served for several years in the U.S. Navy as a yeoman on board the destroyer escort USS Pope (DE-134) in the Atlantic. His ship was still in the Atlantic when the war came to an end with the surrender of Japan in August 1945.

After the war, Gardner returned to UC. He also attended graduate school for a year there, but he did not earn an advanced degree. In 1950 he published an article in the Antioch Review entitled "The Hermit Scientist," a pioneering work on what would later come to be called pseudoscientists. It was Gardner's first publication of a skeptical nature and two years later it was published in a much expanded book version: In the Name of Science, his first book.

In the early 1950s, he moved to New York City and became a writer and designer at Humpty Dumpty magazine where for eight years he wrote features and stories for it and several other children's magazines. His paper folding puzzles at that magazine (sister publication to Children's Digest at the time, and now sister publication to Jack and Jill magazine) led to his first work at Scientific American.

For many decades, Gardner, his wife Charlotte, and their two sons lived in Hastings-on-Hudson, New York, where he earned his living as an independent author, publishing books with several different publishers, and also publishing hundreds of magazine articles and newspaper articles in various magazines and newspapers. Either by choice or coincidence (given his interest in logic and mathematics), they lived on Euclid Avenue.

In 1979, Gardner and his wife semi-retired and moved to Hendersonville, North Carolina. His wife died in 2000. In 2002, he returned to Norman, Oklahoma, where his son, James Gardner, is a professor of education at the University of Oklahoma. He died there on May 22, 2010.

Martin Gardner more or less single-handedly sustained and nurtured interest in recreational mathematics in the U.S. for a large part of the 20th century. He is best known for his decades long efforts in popular mathematics and science journalism, particularly through his "Mathematical Games" column in Scientific American.

Gardner had problems learning calculus and never took a mathematics course beyond high school. He was the editor of a children's magazine named Humpty Dumpty's Magazine for Little Children in 1956 when he was asked by the publisher of Scientific American about the possibility of starting a regular column about recreational mathematics, following his submission of an article about flexagons. The "Mathematical Games" column ran from 1956 to 1981 and was the first introduction of many subjects to a wider audience, including: Flexagons; John Horton Conway's Game of Life; Polyominoes; The Soma cube; The board game "Nash", also called "Hex" and sometimes called "John", independently created by Piet Hein and John Forbes Nash; Hare and Hounds; Tangrams; Penrose tiling; Cryptanalysis/ public key cryptography/ trapdoor ciphers/ the RSA-129 cryptographic challenge; The work of M.C. Escher; Fractals. Many of these articles have been collected in a series of books starting with Mathematical Puzzles and Diversions, first published in 1956.

In 1981, on Gardner's retirement from Scientific American, the column was replaced by Douglas Hofstadter's "Metamagical Themas", a name that is an anagram of "Mathematical Games". Gardner never really retired as an author, but rather he continued to do literature research and to write, especially in updating many of his older books, such as Origami, Eleusis, and the Soma Cube, published 2008. Gardner also wrote a "puzzle" story column for Asimov's Science Fiction magazine for a while in the late 1970s and early 1980s.

Gardner's uncompromising attitude toward pseudoscience made him one of the world's foremost anti pseudoscience polemicists of the 20th century. His book Fads and Fallacies in the Name of Science (1952, revised 1957) is a classic and seminal work of the skeptical movement. It explored myriad dubious outlooks and projects including Fletcherism, creationism, organic farming, Charles Fort, Rudolf Steiner, Scientology, Dianetics, UFOs, dowsing, extra-sensory perception, the Bates method, and psychokinesis. This book and his subsequent efforts (Science: Good, Bad and Bogus, 1981; Order and Surprise, 1983, etc.) earned him a wealth of detractors and antagonists in the fields of "fringe science" and New Age philosophy, with many of whom he kept up running dialogs (both public and private) for decades.

In 1976, Gardner was a founding member of the Committee for the Scientific Investigation of Claims of the Paranormal (CSICOP), and he wrote a column called "Notes of a Fringe Watcher" (originally "Notes of a Psi-Watcher") from 1983 to 2002 for that organization's periodical Skeptical Inquirer. These have been collected in five books: New Age: Notes of a Fringe Watcher (1988), On the Wild Side (1992), Weird Water and Fuzzy Logic (1996), Did Adam and Eve Have Navels (2000), and Are Universes Thicker than Blackberries (2003). Gardner was a senior CSICOP fellow and prominent skeptic of the paranormal. On August 21, 2010, Gardner was posthumously honored with an award recognizing his contributions in the skeptical field, from the Independent Investigations Group during its 10th Anniversary Gala.

Gardner had an abiding fascination with religious belief. He was a theist, professing belief in a Creator God, but critical of organized religion. He has been quoted as saying that he regards parapsychology and other research into the paranormal as tantamount to "tempting God" and seeking "signs and wonders". He stated that while he would expect tests on the efficacy of prayers to be negative, he would not rule out a priori the possibility that as yet unknown paranormal forces may allow prayers to influence the physical world.

Gardner wrote repeatedly about what public figures such as Robert Maynard Hutchins, Mortimer Adler, and William F. Buckley, Jr. believed and whether their beliefs were logically consistent. In some cases, he attacked prominent religious figures such as Mary Baker Eddy on the grounds that their claims are unsupportable. His semi autobiographical novel The Flight of Peter Fromm depicts a traditionally Protestant Christian man struggling with his faith, examining 20th century scholarship and intellectual movements and ultimately rejecting Christianity while remaining a theist. He described his own belief as philosophical theism inspired by the theology of the philosopher Miguel de Unamuno. While critical of organized religions, Gardner believed in God, asserting that this belief cannot be confirmed or disconfirmed by reason or science. At the same time, he was skeptical of claims that God has communicated with human beings through spoken or telepathic revelation or through miracles in the natural world.

Gardner's philosophy may be summarized as follows: There is nothing supernatural, and nothing in human reason or visible in the world to compel people to believe in God. The mystery of existence is enchanting, but a belief in "The Old One" comes from faith without evidence. However, with faith and prayer people can find greater happiness than without. If there is an afterlife, the loving "Old One" is probably real. "[To an atheist] the universe is the most exquisite masterpiece ever constructed by nobody", from G.K. Chesterton, was one of Gardner's favorite quotes.

Gardner has said that he suspects that the fundamental nature of human consciousness may not be knowable or discoverable, unless perhaps a physics more profound than ("underlying") quantum mechanics is some day developed. In this regard, he said, he was an adherent of the "New Mysterianism".

Gardner was considered a leading authority on Lewis Carroll. His annotated version of Alice's Adventures in Wonderland and Through the Looking Glass, explaining the many mathematical riddles, wordplay, and literary references found in the Alice books, was first published as The Annotated Alice (Clarkson Potter, 1960), a sequel published with new annotations as More Annotated Alice (Random House, 1990), and finally as The Annotated Alice: The Definitive Edition (Norton, 1999) combining notes from the earlier editions and new material. The book arose when Gardner, who found the Alice books 'sort of frightening' when he was young but found them fascinating as an adult, felt that someone ought to annotate them and suggested to a publisher that Bertrand Russell be asked; when the publisher did not manage to get past Russell's secretary, Gardner was asked to take the project. The book has been Gardner's most successful, selling over half a million copies.

In addition to the 'Alice' books, Gardner produced “Annotated” editions of Chesterton’s The Innocence Of Father Brown and The Man Who Was Thursday as well as of celebrated poems including The Rime of the Ancient Mariner, Casey at the Bat, The Night Before Christmas, and The Hunting of the Snark; the latter also written by Lewis Carroll.

Gardner occasionally tried his hand at fiction of a kind always closely associated with his non-fictional preoccupations. His roman à clef novel was The Flight of Peter Fromm (1973) and his short stories were collected in The No-Sided Professor and Other Tales of Fantasy, Humor, Mystery, and Philosophy (1987). Gardner published stories about an imaginary numerologist named Dr. Matrix and Visitors from Oz (1998), based on L. Frank Baum's Oz books, which reflected his love of Oz. (He was a founding member of the International Wizard of Oz Club, and winner of its 1971 L. Frank Baum Memorial Award.) Gardner was a member of the all-male literary banqueting club, the Trap Door Spiders, which served as the basis of Isaac Asimov's fictional group of mystery solvers, the Black Widowers.

Gardner was famously shy and declined many honors when he learned that a public appearance would be required if he accepted. However, in 1993 Atlanta puzzle collector Tom Rodgers convinced Gardner to attend an evening devoted to Gardner's puzzle-solving efforts. The gathering was repeated in 1996, again with Gardner in attendance, which convinced Rodgers and his friends to make the gathering a regular event. It has been held since then in even-numbered years near Atlanta, and the program consists of any topic which could have been touched by Gardner during his writing career. The event is called Gathering for Gardner, and is written G4Gn, with n being replaced by the number of the event (the 2010 event thus was G4G9). Gardner only attended the 1993 and 1996 events.

In addition to writing about mathematics, Gardner was an avid controversialist on contemporary issues, arguing for his points of view in a wide range of fields, from general semantics to fuzzy logic to watching TV (he once wrote a negative review of Jerry Mander's book Four Arguments for the Elimination of Television). His philosophical views are described and defended in his book The Whys of a Philosophical Scrivener. Under the pseudonym "George Groth", Gardner panned his own book for the New York Review of Books.

Gardner was known for his sometimes controversial philosophy of mathematics. He wrote negative reviews of The Mathematical Experience by Philip J. Davis and Reuben Hersh and What is mathematics, really? by Hersh, each of which were critical of aspects of mathematical Platonism, and the first of which was well received by the mathematical community. While Gardner was often perceived as a hard-core Platonist, his reviews demonstrated some formalist tendencies. Gardner maintained that his views are widespread among mathematicians, but Hersh has countered that in his experience as a professional mathematician and speaker, this is not the case.