Hall & Partners' former European chief executive Deborah Mills stepped down in October 2009. The role had been overseen on an interim basis by the global chief executive, Vanella Jackson.
Edwards, who is the chairman of the WPP-owned research company TNS, takes up the post next month and will report directly to Jackson, with whom he used to work at Bartle Bogle Hegarty.
His remit includes a focus on growing the company's London business and he will also support the growth and development of Hall & Partners across Europe, the Middle East and Africa.
Edwards was the chief executive and chairman of Lowe UK, before quitting in 2003. He joined Publicis as its UK chief strategy officer in 2004.
His previous senior roles included a spell as the chief executive of the WPP-owned The Henley Centre and planning director at BBH and Young & Rubicam. His client-side experience includes stints at Unilever, Smith & Nephew, and Pedigree Petfoods.
Edwards said: "I am delighted to be joining the Omnicom Group for the first time. I was really attracted by the creativity and the focus of Hall & Partners. I can't wait to meet the teams and get started on our next round of growth."