Marc Laidlaw is an American writer. He is a former lead writer for the video game company Valve, where he worked on the Half-Life series before his departure in 2016. Before joining Valve, Laidlaw was a novelist working in the fantasy and horror genres, and in 1996 won the International Horror Guild Award for his novel The 37th Mandala.

Half-Life is a series of first-person shooter (FPS) games created by Valve. The games combine shooting combat, puzzles and storytelling.