Matt Seiler, the president of PHD North America, has been appointed as global chief executive of Universal McCann, allowing Nick Brien to step up to become president and chief executive of Mediabrands.
Richard Beaven remains global chief executive of Initiative.
Michael Hudes, the global director of digital media for Clear Channel, also joins Mediabrands as president for its diversified media services and strategic development.
IPG said that it had no plans to merge the Initiative and Universal McCann brands.
Its decision to launch Mediabrands marks the second time IPG has attempted to create a media group structure. IPG Media, the previous incarnation, was wound down two years ago.
Brien said: "I am excited by this opportunity to lead an extremely talented, diverse and collaborative leadership team to imagine new approaches for delivery our clients the greatest business impact through media and marketing excellence."