Milligan will report to Ben Essen, the head of planning, and Sam Noble, the chief strategy officer. He will handle strategic leadership for Mini and Domino’s.
At Wieden & Kennedy he worked on the Nike account in Western Europe and on Halls globally. Before this, he was the planning director at Saatchi & Saatchi, the strategy director at Holler and the head of planning at Karmarama.
After starting his career at Rocket PHD, Milligan was at Naked for seven years, working on brands including Selfridges, the COI and Nike.
Essen said: "Ben has been reinventing media for as long as anyone. At Naked he modernised British icons like the Tate, Selfridges and Channel 4. Since then he’s been building brands that people want to get involved with from Nintendo to Nike.
"Ben has a proven track record in creating effective, purpose-driven participation brands. That is at the heart of what we do at Iris."
Milligan, who joins the agency next Monday, said: "I've always admired the work and the culture at Iris. For a while it's been a bit like the best agency you've never heard of, but it's been growing fast, it's full of potential and its time is now.
"There's a big bunch of very smart, very human beings here who are inspired by what can be done, whilst intelligent enough to apply this to what should be done. So I'm looking forward to learning from them and helping them take on what's next."
The Iris planning department has also taken on David Austin, an integrated specialist at Wunderman.