Andy Weitz, president of Hill+Knowlton Strategies US, is exiting the firm to pursue entrepreneurial opportunities and spend more time with his family.
Mike Coates, a 30-year veteran of the WPP unit and CEO of Canada, becomes chief of the Americas region.
The firm says unification of the Americas is part of the global organizational revamp, which is a priority of Jack Martin, who assumed the helm in 2011.
The uncoupling of regions and countries is intended to "allow for localized refinements of structure and process and to provide proving grounds for talent and leadership at all levels and across all geographies," according to H+K.
The Americas move follows the November reorganization of APAC and May reorganization of EMEA.
The group has more than 900 staffers in the US, Mexico, Canada, Guatemala, Brazil, Chile and Argentina.
Coates has led Canada since 1995. Goldy Hyder, president of H+K Canada, will succeed Coates, who will double as US CEO on a temporary basis.