Mirren was born, and grew up, in South London, the only child of a single parent family (her mother, who was a teacher). He left school when he was sixteen and worked in Botswana, Africa building roads. Coming back to the UK, he continue doing odd jobs, until finally he wrote a true story about a close friend of his. That story became a movie called Greenwich Mean Time, which gave him an entry into British TV where he ended working on various shows such as Casualty, Waking the Dead and Spooks/MI5. On Waking the Dead and MI5 was lucky enough to have been a part of both shows from the beginning, acquiring valuable experience for his future endeavors.
Mirren then moved on to writing and producing for American series Third Watch and Without a Trace, until he joined as producer and writer of Criminal Minds after the pilot episode was picked to series. Mirren explains himself how he came to work on Criminal Minds: I was working for Ed Bernero on Third Watch when CBS offered Ed a chance to run a show called Quantico. I read the pilot and immediately recognized the profile part of the show. In Waking the Dead we had a criminal profiler who was based on a real female profiler who I'd met in London. She was an advisor on the show. I thought the profile scenes then lead by Gideon were interesting as they discussed the behavioral traits of the suspect in a way a US audience hadn't heard before. And in discussing behavioral traits they were of course discussing characters.
At this point in TV, studios and networks would put writers in a box and call them procedural or character writers. In Criminal Minds I saw it as chance to have both. Ed asked if I would leave Third Watch and work with him on Quantico. Without hesitation I said yes. Later on the title Quantico was changed to Criminal Minds.
At the end of Season Six, he left Criminal Minds in the wake of he getting a new contract with a different production studio.
Mirren has written the following episodes for Criminal Minds:
- Season One
- Season Two
- Season Three
- Season Four
- Season Five
- Season Six
- Simon is the nephew of British actress Dame Helen Mirren (The Queen, 2006) and director Taylor Hackford.