The move follows the appointment of David King, managing director of Rapp China, as regional CEO for Iris China.
Iris said the Edge partnership gives it access to countries that are important for existing clients Sony Ericsson, adidas and Shell.
Founded in 2004, Edge is led by chairman Patrick Pitcher and chief executive Patrick Looram, with offices in Ho Chi Minh City, Hanoi, Bangkok and Singapore.
Edge acquired New Media, an internet and digital agency in Thailand and Vietnam, in February this year.
In Asia Pacific, Iris has offices in Singapore, Beijing, Delhi, Sydney and Melbourne.
The two agencies have one client in common, Johnnie Walker, with Iris producing campaigns for the drinks brand out of its Singapore office.
Iris said Edge's core specialities - brand strategy, CRM, digital and event marketing for clients such as Mead Johnson, Citibank and Syngenta - complement those of Iris.
London-headquartered Iris lists advertising, digital, direct marketing, sales promotion and experiential as its key functions.
Ian Millner, Iris global chief executive, commented: "Edge and iris are cut from the same cloth - we're independent, we're integrated and we're two very likeminded agencies both in our approach and our ambition to grow our business in a way that meets our clients' requirements".