At the same time, Brett Gosper, currently the co-chairman of Euro RSCG Wnek Gosper, was reported to be taking over as the general manager of McCann's flagship New York office.
Howell, the former HHCL & Partners founding partner, ended weeks of speculation when he was confirmed this week as the president of the network's Europe, Middle East and Africa region and the chairman of its UK and Ireland group.
He replaces Ben Langdon, who was ousted as the regional director of the McCann Worldgroup in June. Howell will share duties with David Warden, the regional director of operations for EMEA, who becomes its chairman.
Warden will have day-to-day control of the region, the largest in the McCann empire, which comprises 104 agencies in 74 countries and controls $8.4 billion worth of billings.
Howell will focus on new business and reinvigorating the London agency.
"London is doing OK but I think I can give it some direction and excitement," he said.
Success in the job could put Howell, 46, in a strong position to succeed John Dooner, the McCann chairman and chief executive, who has indicated he would like to retire within the next three to five years.
Howell's agency career spans spells at Ogilvy & Mather, Grey and Young & Rubicam before he helped found HHCL. He said: "The only thing I've not done in my career is the global bit. I've always been fascinated by big networks."