Stewart revealed his departure publicly in a blog post this week, in which he thanked his former employer by giving it a glowing recommendation
"Square Enix is an amazing company," Stewart wrote, "whether you work for one of its studios or publishing arms, or if you're thinking of joining, this company has given me the opportunity to grow and do what I love to do best, work in creative and ridiculously talented company at the heart of the video game industry. The potential for opportunity and growth at Square Enix is limitless."
Stewart will now bring his expertise to Petrol, an advertising agency that over the last decade has amassed a client list brimming with big-name games companies.
"For the last 8 years I have worked with [co-founders] Alan [Hunter] and Ben [Granados] at Petrol on many different projects, from Batman to Tomb Raider to Thief, and on every occasion they've blown me away with their vision and creativity," Stewart explained. "So when the conversation started about joining the company which they've both worked extremely hard to develop and grow, there was no doubt in my mind this was the right next step for me, as they both think the same way I do. I'm all about experiences, and this is the new experience I'm looking for right now."