O&M, which has worked with AmEx for more than 50 years, will remain on the brand’s agency roster in charge of international execution, the brand confirmed to Ad Week.
As well as responsibility for global brand creative development, Dentsu’s Mcgarrybowen will also be in charge of all US execution of that work.
The changes do not affect O&M's UK relationship with the brand.
Ogilvy has worked with the credit card company since 1962 and was behind the tagline "Don’t leave home without it".
The move comes a year after chief marketing officer John Hayes left to launch AmEx’s new global marketing operations group. He was not directly replaced.