Antony Robbins joins the museum as head of comms from the same role at the Overseas Development Institute, a think-tank on international development.
Robbins has also worked as a comms adviser at the Department for International Development (DfID) and has been head of comms at aid agency CARE International.
He arrives as the museum prepares to launch its £20m Galleries of Modern London and the new Clore Learning Centre, which will tell the story of London from 1666 to the present day.
Robbins will oversee the repositioning of the museum as a world-class destination and manage the museum's external communications team, including marketing, press and online services.
He said: 'My background in international development prepares me well for this role: the museum has a truly global perspective, telling the inspiring story of successive generations of Londoners from across the globe.'