Martin "Marty" O'Donnell (born May 1, 1955) is an award-winning American composer known for his work on video game developer Bungie's series, such as Myth, Oni, and most predominately Halo. O'Donnell collaborates with his musical colleague Michael Salvatori for many of the scores; he has also directed voice talent and sound design for the Halo trilogy, and is currently Bungie's Audio Lead.

O'Donnell began his music career writing television and radio jingles as well as scoring for radio and film. O'Donnell moved to composing video game music when his company, TotalAudio, did the sound design for the 1997 title Riven. After producing the music for Myth II, Bungie contracted O'Donnell to work on their other projects, including Oni and the code-named project that would become Halo: Combat Evolved. O'Donnell ended up joining the Bungie staff only ten days before the studio was bought by Microsoft, and has been the audio director for all Bungie projects since.
O'Donnell's score to the Halo trilogy has been called iconic, and the commercial soundtrack release of the music to Halo 2 became the best-selling video game soundtrack of all time. His most recently released work is the music for Halo: Reach, released digitally on September 14, 2010.