Langdon will continue in his role as the chairman and chief executive of McCann-Erickson World Group EMEA, but will assume greater involvement in the running of the UK agency.
McCann maintains that Ingram's departure came after she turned down a new role, which took her away from the core advertising business.
Langdon said: "The structural changes I want to make in the UK and in other markets across Europe would have meant that she would have had to concentrate on developing the non-advertising parts of McCann's business in the UK. She didn't want to do this, so we have decided to call it a day."
An announcement concerning a direct replacement for Ingram is expected in the coming weeks. This will be coupled with details of a restructure, which will see Ingram's successor take more responsibility for McCann's non-advertising interests while working far more closely with Langdon.
Speculation has persisted that Langdon was dissatisfied with the agency's new-business record last year, as well as Coca-Cola's decision to turn to Mother for new ideas and some reported dissent from the agency's client Nestle.
However, industry observers are surprised that Ingram only had 12 months to make an impression. In the latter part of 2002, she made senior staffing changes, which are only now settling down.
Bob Willott, the editor of Marketing Services Financial Intelligence, said: "When organisations the size of IPG have got problems in one part of the world, they put the squeeze on other parts. This puts huge pressure on anyone who has just got their feet under the desk."