O'Sullivan and Jones set up what was Blue Rubicon's consumer brand offshoot in March 2012, and he then left the agency in August 2015.
In his new role, which began earlier this month, he reports to Bell Pottinger chair of the corporate, brand, digital, consumer and design practices, Kevin Read. The businesses run by Read stand alongside the firm's better-known financial, political, international and governmental offerings.
Read said: "One of the things that we're finding from our clients is that they're coming to us with challenges that they want us to solve in a channel-agnostic way, and they're also putting a very high premium on creative thinking."
A statement from the agency said O'Sullivan "will be responsible for supporting new and existing clients in their creative ambitions" and working across the areas overseen by Read to "evolve cutting-edge creative approaches, training and products". His initial responsibilities include reviewing how Bell Pottinger's new business operation works, Read said.
Read also said: "After an extensive search we are delighted to have Kev on board for what is set to be a highly exciting and creative 2016. His appointment is another example of our commitment to innovation in content, engagement and communications."
O'Sullivan, who had worked at Blue Rubicon since 2008 before launching Surname & Surname, latterly as an associate director, said: "When you get the call from Bell Pottinger, you take it."