Pendleton served in the U.S. Navy during World War II, serving in all theaters of the war. His enlistment ended in November 1947. He returned to active duty in 1952 during the Korean War and served until 1954. He worked as a telegrapher for the Southern Pacific Railroad until 1957, and then as an air traffic control specialist for the Federal Aviation Administration. In the 1960s, he worked for Martin Marietta on the Titan missile program. He later served as an engineering administrator at NASA during the Apollo missions. Pendleton also worked on the C-5 Galaxy transport aircraft program.

The best-selling The Executioner made the men's action-adventure genre popular in the late 1960s and 70s, and Pendleton was known as the father of action adventure, a term he coined. The Mack Bolan novels penned by Pendleton revolved around Bolan's one man war against the Mafia, beginning with War Against the Mafia in 1969, and ending with Satan's Sabbath in 1980. After Satan's Sabbath, Pendleton licensed the rights to his Executioner characters to the Harlequin publishing group. Since 1980, The Executioner, Mack Bolan books and spinoffs, Able Team, Phoenix Force, Stony Man, Mack Bolan have been written by Harlequin's team of writers. The Harlequin Gold Eagle books moved Bolan into a fight against terrorism. Since 1980, Harlequin has produced new novels and the writer's name is mentioned on the copyright page as a provider of "a contribution" to the work, pushing the number of Mack Bolan novels into the hundreds; all of them bear the byline, Don Pendleton's Mack Bolan. Other works by Don Pendleton after 1980 include the Joe Copp, Private Eye series of six novels, the Ashton Ford, Psychic Detective series of six novels, and nonfiction books. He collaborated on several books with his wife, Linda Pendleton, including their popular nonfiction book, To Dance With Angels. His earlier writings in the 1960s include mysteries, Sci-Fi and futuristic books.

In the pulp tradition, Pendleton's Mack Bolan was larger than life, responsible for killing literally hundreds of mobsters over the course of his original thiry-eight novels. Also in the pulp tradition, he left a trademark "calling card", a marksman's medal, wherever he struck. Many see similarities between the Executioner and Marvel Comics' The Punisher and Marvel freely acknowledge they took some inspiration from the novels in creating their antiheroic character. Bolan also inspired DC Comics' The Vigilante.

After fifteen Executioner novels, Pendleton became involved in a legal battle with the publisher, Pinnacle Books, over ownership of the series. Pinnacle had the next entry, The Executioner #16: Sicilian Slaughter, written by an unknown writer under the pseudonym "Jim Petersen". Pendleton wrote what was published as #17, Jersey Guns, as his own sequel to # 15, Panic in Philly under a new contract with New American Library, which was ultimately voided by the terms of his settlement with Pinnacle, and he returned to the Bolan character for twenty-one more novels.

Pendleton's other enduring series was the Joe Copp, Private Eye novels, told in the first person by 6'3", 260 lb. Joe Copp, a private investigator. The novels were formulaic hardboiled detective fiction, always opening in the middle of the story, with Copp pursuing a variety of criminals, the story then flashing back to the beginning to describe how Copp got into his current predicament. The Joe Copp series of six hardcover novels often had over-the-top action moments reminiscent to those found of Mickey Spillane's Mike Hammer. The books were first published in hardcover by Donald I. Fine, and then released in paperback by Harper. Now in Kindle.

Don Pendleton's Ashton Ford, Psychic Detective series, the first, Ashes to Ashes was published in 1986 by Warner Books. Currently four of the Ashton Ford novels and the Joe Copp novels are on Audio CD through Books in Motion. Pendleton's Ashton Ford character is a former naval officer and spy, skilled in cryptology and with the ability to see into the future. Now in Kindle.

Both the Joe Copp Thrillers and the Ashton Ford Psychic Detective series, now available in Kindle, at amazon.com

Pendleton wrote several of his earlier, non-Executioner books under the pseudonyms Dan Britain and Stephan Gregory.

Mack Bolan novels

• War Against The Mafia (1969)
• Death Squad (1969)
• Battle Mask (1970)
• Miami Massacre (1970)
• Continental Contract (1971)
• Assault on Soho (1971)
• Nightmare in New York (1971)
• Chicago Wipe-Out (1971)
• Vegas Vendetta (1971)
• Caribbean Kill (1972)
• California Hit (1972)
• Boston Blitz (1972)
• Washington I.O.U. (1972)
• San Diego Siege (1972)
• Panic In Philly (1973)
• Jersey Guns (1974)
• Texas Storm (1974)
• Detroit Deathwatch (1974)
• New Orleans Knockout (1974)
• Firebase Seattle (1975)
• Hawaiian Hellground (1975)
• Canadian Crisis (1975)
• St. Louis Showdown (1975)
• Colorado Kill-Zone (1976)
• Acapulco Rampage (1976)
• Dixie Convoy (1976)
• Savage Fire (1977)
• Command Strike (1977)
• Cleveland Pipeline (1977)
• Arizona Ambush (1977)
• Tennessee Smash (1978)
• Monday's Mob (1978)
• Terrible Tuesday (1979)
• Wednesday's Wrath (1979)
• Thermal Thursday (1979)
• Friday's Feast (1979)
• Satan's Sabbath (1980)

• The Executioner's War Book (1977) "technical manual" and history of the War against the Mafia

Joe Copp, Private Eye Novels

• Copp for Hire (1987)
• Copp on Fire (1988)
• Copp in Deep (1989)
• Copp in the Dark (1990)
• Copp on Ice (1991)
• Copp in Shock (1992)

Ashton Ford, Psychic Detective Series

• Ashes to Ashes (1986)
• Eye to Eye (1986)
• Mind to Mind (1987)
• Life to Life (1987)
• Heart to Heart (1987)
• Time to Time (1988)

Fiction With Linda Pendleton

• Roulette
• War Against the Mafia Graphic Comic Novel Adaptation Part 1-3. Part 4 not published.

Nonfiction With Linda Pendleton

• Whispers from the Soul: The Divine Dance of Consciousness
• The Metaphysics of a Novel: The Inner Workings of a Novel and Novelist
• To Dance With Angels
• The Cosmic Breath: Metaphysical Essays of Don Pendleton

Nonfiction by Don Pendleton

• A Search for Meaning From the Surface of a Small Planet

Stewart Mann Novels by Stephan Gregory

• Frame Up. Fresno, 1960.
• The Insatiables, 1967.
• The Sex Goddess, 1967.
• Madame Murder, 1967.
• The Sexy Saints, 1967.
• The Hot One, 1967.

Other Novels by Don Pendleton

• All the Trimmings (as Stephan Gregory), 1966.
• The Huntress (as Stephan Gregory), 1966.
• Color Her Adultress (as Stephan Gregory), 1967.
• All Lovers Accepted (as Stephan Gregory), 1968.
• Revolt, 1968.
• The Olympians, 1969.
• Cataclysm, 1969.
• The Guns of Terra 10, 1970.
• Population Doomsday, 1970.
• The Godmakers (as Dan Britain, reissued as Don Pendleton), 1970.
• Civil War II, (as Dan Britain, reissued as Don Pendleton), 1971.