Cater has been the practice's associate director for the past two years, based in London, and will relocate to New York to assume his new role from 20 April.
He takes the position from David Catlett, who assumes a newly created role of healthcare client service and development director.
Ketchum Europe CEO Jon Higgins said: 'Mark will continue to have oversight of the European business from New York but it's anticipated that UK healthcare managing director Avril Lee will take on a broader role here as our UK and European business expands.'
Catlett has directed Ketchum's global healthcare practice for eight years.
In a statement the agency said the changes were partly aimed at 'providing fresh challenges for two principal healthcare players'.
Most recently Cater, who joined Ketchum three and a half years ago, led the agency's support of the Global Health Initiative on behalf of the World Economic Forum.
His promotion heralds a return to a US-based role - he joined Ketchum from medical education group OCC North America.