Born in Bristol, Marshall joined the Bristol music scene as a member of the sound system The Wild Bunch in the 1980s, which included two other Massive Attack members, Robert del Naja and Andrew Vowles. At the time he was one of the youngest DJs in the city. In 1986, The Wild Bunch disbanded. Del Naja, Vowles, and Marshall then formed the trip hop group Massive Attack, which is considered to have pioneered the Bristol Sound along with Portishead and Tricky.
In addition to appearing on Massive Attack's albums, Marshall has also mixed a CD for the DJ-Kicks mix series.