A prolific electronic composer of music for television and film. His work includes the arrangement of the Doctor Who theme music which served as the series' theme for Season 23 of the programme. He also wrote the incidental music for the Doctor Who stories The Mysterious Planet, The Ultimate Foe, Dragonfire, The Happiness Patrol and Survival.

Glynn has a long-term working relationship as composer for the films of British filmmaker Anthony Baxter, which began with the 2011 documentary You've Been Trumped. Subsequent films include A Dangerous Game (2014), You’ve Been Trumped Too (2016), Flint: Who Can You Trust (2020) and Eye of the Storm (2021) which won the British Academy Scotland Award for Specialist Factual in 2021. Glynn was a guest of honour at the science fiction convention ArmadaCon in November 2024.