Michael Barrington, 58, the chairman, and Steve Johnson, 59, its creative chief, will both retire by the end of the year but will retain a small amount of equity.
Trevor Lorains, the third founding partner who helped establish the Manchester shop in 1987, remains as the managing director with a new team of directors.
They are Jane Clancy, Jackie Holt, Nicky Unsworth and Iain Kerr, the finance director. They will share the remaining equity almost equally.
The 70-strong agency runs British Airways' regional advertising. Its other major clients include Littlewoods, Eurocamp and Pilkington.
The "buy in" marks the arrival of the next generation of management who will take the agency forward 17 years after its founders broke away from J. Walter Thompson in Manchester to launch their start-up. All three had made their names on JWT's Asda business and were responsible for developing the supermarket chain's long-running "Asda price" ad theme.
Barrington, who plans to work on a number of writing projects, said the succession management plan had been in place for some time. "Our strong culture has proved that common sense and creativity can be mutually inclusive and I'm sure that will endure," he said. "This is very much an evolution with Trevor providing the bridge between the old and new management."
Lorains said: "The new team will help to build on Barrington Johnson Lorains' excellent reputation."