Brien, who will report to the chairman and chief executive of IPG's media operations, Mark Rosenthal, rather than McCann Worldgroup's chairman and chief executive, John Dooner, said: "I have no ambition to come in and sever and separate in any fashion but the nature of the relationship (with McCann) will change."
He added that it was too early to provide details on this but that Universal's operations and finances would report directly to IPG Media, which was created last year.
Brien, 43, joins Universal in October from the Publicis below-the-line network Arc Worldwide, where he has been the chief executive since February 2004.
Before this, he was the president of corporate business development for Starcom MediaVest Group in Chicago after running Leo Burnett London as its chief executive. He joined Leo Burnett in 1992, having been a founder of the media agency BBJ.
He replaces Robin Kent, who moved to a McCann Worldgroup role in March. Murray Dudgeon, who was caretaking the post, returns to his position of chief operating officer. Arc is replacing Brien with Marc Landsberg, previously its president.
Brien's arrival follows a rocky new-business period for Universal, which has lost the General Motors buying account in the US and L'Oreal Golden across Europe. However, Brien said: "It (Universal) has strengths and weaknesses just like any other network. I need to listen to clients and key staff and arrive at an analysis of those strengths."
Rosenthal said: "Brien is more than just a top-tier international media executive. He brings a unique breadth of experience, having led an ad agency and multi-disciplinary marketing services company. He's known as a passionate client partner who understands the big picture."
- Opinion, page 19.