Walter Brown Gibson was born on September 12, 1897, in the Germantown neighborhood of Philadelphia, Pennsylvania, to Alfred Cornelius Gibson (1849—1931) and May Morrell Whidden Gibson (1863—1941).

Gibson graduated from Colgate University in 1920 where he was a brother of Delta Kappa Epsilon, and began working "for newspapers in his native Philadelphia as a reporter and crossword-puzzle writer," specifically for the Philadelphia North American, and later The Evening Ledger. In 1928 Gibson was asked by Macfadden Publications to edit True Strange Stories; he did, for a time, identified as Walter Scofield, commuting back and forth to New York. In 1931, after submitting some crime stories for Detective Story Magazine, he was asked by publishers Street & Smith to produce the first print adventure of wealthy playboy Lamont Cranston, who, voiced by James La Curto, had risen to prominence in his guise as The Shadow, the character who narrated the Detective Stories radio drama.

The popularity of the radio show's narrator inspired the show's sponsors (Street & Smith) to translate the character into print, and Gibson was duly asked to produce 75,000 words for the first quarterly issue of The Shadow pulp magazine. This first Shadow story was published on April 1, 1931, just nine months after the character's appearance on the airwaves. Six months later, The Shadow was headlining a new radio show, and his pulp adventures...written by Gibson under the house pseudonym Maxwell Grant...were going from strength to strength. Although launched as a quarterly publication, "within months, the magazine was on a twice-monthly schedule," causing Gibson to produce the equivalent of 24 novels per year. Described as a "compulsive writer," Gibson is estimated to have written, at his peak, 1,680,000 words a year, and at least 282 of the 325 Shadow novels.

As the character spun off into "comic strips, movies, reruns and parlor games," Gibson went with him, scripting some of the comic book and strip cartoons and serving as consultant on the Sunday night radio show.

Gibson is recognized as the creator of much of The Shadow's mythos, although his tales often conflict with the better-known radio version. For example, Gibson's Shadow is, in reality, Kent Allard, an aviator, who sometimes posed as playboy Lamont Cranston. On the radio, The Shadow really is Cranston, a "wealthy young man about town." Similarly, Shadow companion Margo Lane arose not from the pulps but from the radio program; she was added to offer a contrasting female voice. In 1941, Gibson grudgingly added Margo Lane to the pulp novel stories and even hinted at a power of invisibility.

Gibson wrote more than a hundred books on magic, psychic phenomena, true crime, mysteries, rope knots, yoga, hypnotism, and games. He served as a ghost writer for books on magic and spiritualism by Harry Houdini, Howard Thurston, Harry Blackstone, and Joseph Dunninger. Gibson also introduced the famous "Chinese linking rings" trick in America, and invented the "Nickels to Dimes" trick that is still sold in magic stores to this day. He "wrote extensively on Houdini and his escape tricks and sleight-of-hand," and became involved after Houdini's death with seances. Houdini was known as much for his investigations into ... and exposure of ... false mediums, and after his death, his wife Bess held seances for ten years in an attempt to contact the deceased magician. She then passed this role on to Gibson, who for many years helped preside over the Houdini Seances at New York's famous Magic Towne House with such well-known magicians as Milbourne Christopher, Dorothy Dietrich, Bobby Baxter, and Dick Brooks. Before Gibson died, he passed on the responsibility to Dietrich, currently of The Houdini Museum in Scranton, Pennsylvania.

Under the pen name Andy Adams, Gibson is credited with writing at least five of the twelve novels in the Biff Brewster juvenile adventure and mystery series for adolescent boys: Brazilian Gold Mine Mystery, Mystery of the Mexican Treasure, Mystery of the Ambush in India, Egyptian Scarab Mystery, and Mystery of the Alpine Pass.

With his wife Litzka R. Gibson (née Gonser), he co-wrote The Complete Illustrated Book of the Psychic Sciences (Doubleday, 1966), a 404-page book which explains how to practice many popular forms of divination and fortune-telling, including astrology, tasseography, graphology, and numerology. Litzka also wrote her own books on topics as diverse as palmistry, dancing, and personal hygiene, sometimes under the pen-name Leona Lehman.

He is a featured character in the Paul Malmont novel The Chinatown Death Cloud Peril, which was published by Simon & Schuster in 2006. In addition, Gibson is the protagonist, along with Orson Welles, in a historical mystery by Max Allan Collins, The War of the Worlds Murder, published by Berkley Books in 2005.

While not appearing directly, in P. N. Elrod's "Bloodlist," Jack Fleming mentions that he knows the author of the Shadow Magazine, and when he comes across a mobster guard reading "Terror Island" thinks to himself that he'll "have to write to Walter and tell him about his mobster fan."