King replaces the outgoing Mike Dodds, who accepted the role of chief executive at Proximity last month.
Sam Williams-Thomas, the deputy managing director and head of new business, will become the managing director.
In her new position, King will be responsible for a number of major accounts, including BT, British Airways and Cancer Research UK.
She is expected to take up her new role as soon as she returns from maternity leave later this month.
Since joining Ogilvy from Wunderman's New York office in 1998, King has held several roles, including client service director, head of interactive, and deputy managing director. She was appointed to the position of managing director in October 2007.
In that role, King was instrumental in securing a number of major accounts for the agency, including British Airways and British Gas.