The appointment follows the recent promotion of Michael Frohlich to EMEA CEO – after Frohlich initially retained the role of UK CEO.
Manson has spent the last two years as EMEA MD of Social@Ogilvy.
Stuart Smith, global CEO of Ogilvy PR, said: "Marshall has repaid all the faith we placed in him with massive interest. I am delighted he will use his considerable talents to take Ogilvy PR UK on the next leg of its expansion."
Before joining Ogilvy, Manson was EMEA MD of digital for Edelman, where he built large and successful businesses in both London and Washington, DC. Prior to this he worked in US politics, where he focused on strategy, media relations and copywriting.
Frohlich said: "Marshall brings extraordinary talent to Ogilvy. He delivers success for our clients and our business in spades. He is known not only as a world-class strategist creating winning social media solutions, but also as a respected mentor and leader, making great waves in a very short time to improve our social capabilities across the Ogilvy Group UK and EMEA."
Manson said: "I couldn’t have been more pleased to be asked by Stuart and Michael to take on the role of UK CEO. This business has shown incredible growth and change over the past three years, but I know we have so much more potential to be realised."
Ogilvy PR is also moving offices to Sea Containers House on the Southbank in January next year.
Manson added: "Our imminent move opens up the possibility of new specialisms, offering greater content capabilities and seamless integration with our fellow Ogilvy companies. I cannot wait to share this new space with our partners, and watch our teams enjoy even more innovative ways of working. The future is bright for this business and I am thrilled to be at the helm of it as we move towards 2016 and beyond."
Marshall Manson will retain his EMEA social remit while Social@Ogilvy global managing director Thomas Crampton leads the search for a successor.