Susman will advise the global senior team as non-executive chairman of DJE Holdings - parent company of Edelman and Zeno Group.
Before being named ambassador in 2009, Susman was MD and vice-chairman of Citigroup Corporate and Investment Banking. He also played a major role in fundraising for the Barack Obama presidential campaign.
Richard Edelman, CEO and president of Edelman, pointed to Susman’s business acumen as a key motivation behind the appointment.
‘The competitive context is changing, and we are increasingly scrumming with advertising agencies and digital agencies among others for money. The strategic choices are not obvious and that’s why I need a guy such as Louis who has great judgement.
‘Globally, this strategic element is particularly challenging and though we are number one in the US, we want to improve our market position in places like Europe.’
The move follows the death of Richard Edelman's father and the agency's founder Daniel J Edelman in January.
Of Susman, Edelman added: ‘I had worked with my dad for 35 years and he is the closest approximation, except he is 20 years younger. He will always tell me the straight story and will be a great counsellor for me as we try to build this business.’
Susman’s political background includes being appointed to the US Advisory Commission on Public Diplomacy by Ronald Reagan in 1988.
In 2004, he was John Kerry’s national finance chairman and later was a senior adviser to President Obama during his 2008 presidential campaign.
Susman added: ‘I am a family friend and I have great admiration for the company. When Richard approached and suggested I join it sounded interesting and fun, and I liked the idea it was a global role. Communications is a growing and exciting field and though the running of the business and details will be led by Richard, I will be offering counselling where needed.’
Richard Edelman told PRWeek last year that the agency was increasingly focusing on growing its research arm.