Iris and Cheil announced the partnership shortly after midnight today and stated that both companies would remain as separate entities.
The two companies envisage an "East meets West" agency network allowing both to extend into new markets around the world.
Iris, which looks after Guinness, Samsung and Diageo, said Cheil’s investment would "potentially rise to 100 per cent of the business over the next five years".
Iris could not comment on the initial level of Cheil’s investment but it replaces the US publisher Meredith as a shareholder, which formerly owned 20 per cent of the company.
Ian Millner, joint chief executive at iris, said: "We are about to enter the most exciting chapter for iris. This partnership won’t change who we are or what we do as a creative innovation network – but will extend our global reach and capabilities, and enable our clients and people to benefit from the huge opportunity presented by a true ‘East Meets West’ and ‘West Meets East’ network."
Cheil has 5,000 employees and operates from 48 offices in 41 countries while iris has 1,000 employees with 17 offices around the world.
Cheil was advised by Results International and Linklaters while iris was advised by Osborne Clarke and BDO.
Daiki Lim, president of Cheil Worldwide, said: "Our goal was to find the right partner who could match our determination and drive. We've watched with awe how iris has built its global business and we are delighted to have this opportunity to work with its brand."