Before entering the games industry, Stephen trained at Goldsmiths College in London and spent nine years working within the audio industry. In 1995, he worked on the film Eye of the Beholder. He subsequently became the audio director of the United Kingdom branch of Acclaim Entertainment. In this role, he was responsible for the music of classics such as Alien Trilogy, Die Hard, Hexen, and the Extreme-G series. Along with Dominic Glynn, Root also formed the The Swarm. The pair scored the atmospheric electronic scores to Forsaken and Re-Volt together.

In 2001, Root joined Guildford game developer Criterion Games as senior orchestrator. During his six years at Criterion he has successfully built up one of the most highly regarded audio teams in the industry and ensured that his teams deliver outstanding and critical acclaimed content. He and Steve Emney were responsible for creating the music for Airblade, Burnout, and Burnout 2.

Following Criterion's acquisition by EA, Root has remained audio director of the company, but no longer personally produces compositions. The latest Burnout titles have featured licensed music chosen by EA in Los Angeles. Black featured an acclaimed orchestral score by Chris Tilton and Michael Giacchino overseen by Root. Root nevertheless continues to create compositions in his spare time and recently scored the film The Crate.