The former director of Kinetico International and head of digital at British Gas Home Services will work alongside founder and CEO Petra Clayton.
He is charged with supporting the growth of the business "with the implementation of strategic, results-driven initiatives that underpin the consultancy’s well-recognised capabilities".
Simpson has also worked at Tyco Integrated Fire and Security services as a head of channel and digital marketing in a six-year stint.
Clayton said the Woking-based agency had more than 140 applications for the role.
"Custard has been going through some very exciting changes over the last few years and we’ve developed into a serious consultancy to make a real difference to our clients," she said.
"To continue moving forward, we needed someone to help support my role and to help grow the company and provide more for our valued hotel and venue clients across the UK."
Simpson added: "As someone who is new to the hospitality industry, I’m keen to utilise my multi-sector experience to reinforce Custard’s already strong reputation, as well as support our clients’ performance. I look forward to working alongside Petra and leading Custard’s brilliant team of marketing and PR professionals."