The deal will see the joint managing directors of Concise - Benjamin Chilcott, James George and Josh Thomson - receive a 70 per cent up front cash payment, with the remaining 30 per cent paid as shares in Iris.
Concise will continue to function under its original name, but will operate as part of the Iris group. The founders will retain their job titles, and will report to Ian Millner, the chief executive of Iris.
The acquisition is the first in Iris' nine-year history and marks a shift in the agency's offering towards a more integrated model addressing clients' broader business issues.
Millner said: "Concise gets to the heart of clients' business needs and our relationship with them allows us to develop a much deeper understanding of where we can add value."