Smith, who has most recently been consulting for a range of brand and agency clients in Australia, will work alongside board directors Kathryn Smith and Vicki Harding.
Iris Culture managing director Laura Weston said that Smith, who starts on 9 July, would take on some of her responsibilities, together with the rest of the senior leadership team, while she is on maternity leave.
She added: "Ben's focus will be very much on new business and creative rather than the overall running of the agency."
Smith started his career as a planner in Saatchi & Saatchi’s European network before setting up the Sydney office of Splendid Communications with founding client Smirnoff.
He then returned to London for a two-year stint heading the communications team at Exposure Europe before heading back to Australia as a senior consultant.
"I have always been a fan of Iris’ integrated work and had been looking for the right route to return to London," said Smith. "The team is whip-smart, with exactly the type of clients that excite me. I’m thrilled that Iris Culture continues to invest in creativity and innovation at the heart of its business and am looking forward to joining the firm."
Weston added: "Ben shares our passion for conceiving insight-led, big creative ideas for brands and his vast agency experience from around the world will be invaluable to us. We are looking forward to him having a long career at iris to help drive growth both in the UK and the wider global network."