Robertson was previously a partner and MD in charge of corporate, technology and public affairs at the firm, which she joined in 2011, while Murphy was previously a senior managing director and partner.
As deputy CEO, Robertson will be responsible for leading and directing the practices and for the daily management and operations of Ketchum's London business. She will maintain her current role as head of new business.
New COO Murphy will work with senior leadership in London and Europe to further expand and develop Ketchum London’s services. She has been with the firm for nearly 15 years.
Denise Kaufmann, partner and CEO of Ketchum London, said: "Deirdre and Jo-ann are both highly strategic leaders with proven track records in business generation. As two of our best client counsellors, they have each made significant contributions to the success of the London office and have been champions of integration, flexible teams and putting clients at the centre of what we do."