Capella was appointed by the company, which employs more than 450 people across 11 offices worldwide, following a three-way pitch.
The brief is to tell Marin’s story to the national and trade media, and ensure the company leads the debate over the future of advertising.
The account will be led by Capella PR agency founder, Gareth Thomas, and was previously held by Thomas’ former employer Brands2life, which did not repitch.
Marin manages more than £2.5bn in spend for some of the world’s largest brands and media agencies.
Its platform seeks to reduce the complexity facing advertisers as they run campaigns across multiple channels including search, display and social media, as well as different devices including mobile and tablets.
Thomas launched Capella PR in July after leaving his role as director and head of digital at Brands2Life.
He said: ‘Online advertising enjoys highest share of UK ad spend, putting Marin at the heart of how companies acquire customers and revenue today. We're looking forward to getting Marin the media attention it deserves in 2013.’