Morris has written and edited over fifty novels, novellas, short story collections and anthologies. His script work includes audio dramas for Doctor Who, Jago & Litefoot and the Hammer Chillers series. His most recent work includes the Obsidian Heart trilogy (The Wolves of London, The Society of Blood and The Wraiths of War), the original Predator novel Stalking Shadows (co-written with James A. Moore), the official novelization of the Doctor Who 60th anniversary special Wild Blue Yonder, new audio adaptations of the classic 1971 horror movie Blood on Satan's Claw and the M.R. James ghost story A View From a Hill, a 30th anniversary short story collection Warts And All, and, as editor, the anthologies After Sundown, Beyond the Veil, Close to Midnight and Darkness Beckons. Blood on Satan's Claw won the New York Festival Radio Award for Best Drama Special, and A View From a Hill won the New York Festival Radio Award for Best Digital Drama Program, and was also awarded Silver at the 2020 Audio & Radio Industry Awards. Mark has won two British Fantasy Awards, and has also been nominated for several Stokers and Shirley Jackson Awards.