Debra Doyle was born in Florida and educated in Florida, Texas, Arkansas, and Pennsylvania—the last at the University of Pennsylvania, where she earned her doctorate in English literature, concentrating on Old English poetry. While living and studying in Philadelphia, she met and married her collaborator, James D. Macdonald, and subsequently traveled with him to Virginia, California, and the Republic of Panamá. Doyle and Macdonald left the Navy and Panamá in 1988 in order to pursue writing full-time. They now live in a big 19th-century house in Colebrook, New Hampshire, where they write science fiction and fantasy for children, teenagers, and adults. They have collaborated on many novels, including the Circle of Magic series: School of Wizardry, Tournament and Tower (= Secret of the Tower), City by the Sea (= The Wizard's Statue), The Prince's Players (= Danger in the Palace), The Prisoners of Bell Castle (= The Wizard's Castle), The High King's Daughter (all Troll Books, 1990), Mystery at Wizardry School (Hodder, 2003) and Voice of the Ice (Hodder, 2004); the Mageworlds series from Tor: The Price of the Stars (1992), Starpilot's Grave (1993), By Honor Betray'd (1994), The Gathering Flame (1995), The Long Hunt (1996), The Stars Asunder (1999), and A Working of Stars (2002); and the Bad Blood series from Berkeley: Bad Blood (1993), Hunters' Moon (1994), and Judgment Night (1995). Other novels include Knight's Wyrd (Harcourt Brace, 1992; Mythopoeic Aslan (YA) Award winner), Vampire's Kiss (Harper, 1994 as by Nicholas Adams), and Groogleman (Harcourt Brace, 1996). Under the pseudonym Douglas Morgan, they published the military technothriller Tiger Cruise (Forge, 2000) and a collection of annotated sea chanties, What Do You Do With a Drunken Sailor (Swordsmith, 2002). James D. Macdonald is also the author of The Apocalypse Door (Tor, 2002). Their most recent works are alternate-historical fantasies set during the Civil War, from Eos: Land of Mist and Snow (2006), and Lincoln's Sword (2010).

They have written a number of ties, just a few under their own names: Robert Silverberg's Time Tours 3: Timecrime, Inc. (Harper, 1991), Daniel M. Pinkwater's Melvinge of the Megaverse 2: Night of the Living Rat (Ace, 1992), and Gene Roddenberry's Earth: Final Conflict 3: Requiem for Boone (Tor, 2000). As Robyn Tallis they wrote Planet Builders 2: Night of Ghosts and Lightning (Ivy, 1989), and 5: Zero-Sum Games (Ivy, 1989). As Nicholas Adams they wrote Horror High 7: Pep Rally (Harper, 1991). As Victor Appleton: Tom Swift 5: Monster Machine and 6: Aquatech Warriors (both Pocket, 1991). As Martin Delrio: Mortal Kombat (Tor, 1995), Spider-Man Super-thriller 1: Midnight Justice and 3: Global War (both Pocket, 1996), Prince Valiant (Avon, 1998), and Battletech Warrior: MechWarrior Dark Age 4: A Silence in the Heavens, 5: Truth and Shadows, and 6: Service for the Dead (all Roc, 2003).

Their story "Philologos; or, A Murder in Bistrita" appeared in the 9th Year's Best Fantasy (Hartwell and Cramer, eds.). Other stories have appeared in Werewolves (Yolen, Greenberg, eds.), Vampires (Yolen, Greenberg, eds.), Newer York (Watt-Evans, ed.), Alternate Kennedys (Resnick, Greenberg, eds.), Bruce Coville's Book of Monsters (Coville, ed.), Bruce Coville's Book of Ghosts (Coville, ed.), Bruce Coville's Book of Spine Tinglers (Coville, ed.), A Wizard's Dozen (Stearns, ed.), A Starfarer's Dozen (Stearns, ed.), Witch Fantastic (Resnick, Greenberg, eds.), Swashbuckling Editor Stories (Betancourt, ed.), Camelot (Yolen, ed.), The Book of Kings (Gilliam, Greenberg, eds.), Tales of the Knights Templar (Kurtz, ed.), On Crusade: More Tales of the Knights Templar (Kurtz, ed.), Alternate Outlaws (Resnick and Greenberg, eds.), Otherwere (Gilman and DeCandido, eds.), A Nightmare's Dozen (Stearns, ed.), Not of Woman Born (Ash, ed.), Crusade of Fire (Kurtz, ed.), and Cosmic Tales II (Weiskopf, ed.).