The event, which comes to London in 2009, is the ATP World Tour's season-ending championship and features the world's top eight ranked singles players battling to be the number one player of the year.
The world's top eight doubles teams will also be competing to establish the top pairing.
The finals, which have been hosted by cities including New York, Sydney, Stockholm and Lisbon in the past, will be held at the O2 Arena annually from 2009 until at least 2012.
Phil Anderton, chief marketing officer of the ATP, said: "We'll be working closely to both develop and market the event across all channels.
"Publicis' ability to ignite conversations should insure there is a huge buzz around what we are sure will become one of the countries 'must-see' annual sporting fixtures."
Roger Federer, ranked world number two, said: "[I am] delighted that the end of season championships will be moving to one of my favourite cities in the world. I'm sure it will be a spectacular event in what looks like a fantastic venue."
Earlier this year Barclays signed a £17.5m five-year deal with ATP to become title sponsor of the end-of-season finals from 2009.
The event has been renamed the Barclays ATP World Tour Finals and will replace the Tennis Masters Cup, which is currently held in Shanghai's Qi Zhong Tennis Center.