Martin O'Donnell (born May 1, 1955) is an American composer, audio director, and sound designer known for his work on video game developer Bungie's titles, such as the Myth series, Oni, the Halo series, and Destiny. O'Donnell collaborated with his Michael Salvatori for many of the scores; he has also directed voice talent and sound design for the Halo trilogy.

O'Donnell began his career in music writing television and radio jingles such as the Flintstones Chewable Vitamins jingle and scoring for radio stations and films. 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 project that would become Halo: Combat Evolved. O'Donnell ended up joining the Bungie staff ten days before the studio was bought by Microsoft, and was the audio director for all Bungie projects until he was fired in April 2014.

O'Donnell's score to the Halo trilogy has received critical acclaim, earning him several awards, and the commercial soundtrack release of the music to Halo 2 was the best-selling video game soundtrack of all time in the United States. He composed the scores for Halo 3 (2007), Halo 3: ODST (2009), and Halo: Reach (2010). His final work for Bungie was composing music for the 2014 video game Destiny. He successfully sued Bungie for unpaid wages and stock ownership. Subsequently, he co-founded Highwire Games and composed the score for their debut virtual reality game Golem, which was released in late 2019.

O'Donnell unsuccessfully ran for the U.S. House of Representatives as a Republican in Nevada's 3rd congressional district in 2024, placing fourth in the Republican primary.