They assume the title alongside Leon Jaume, who continues in his role of executive creative director of WCRS as well as the wider Engine group.
Neil and Faithfull were made creative directors in 2011, with responsibility for the day-to-day running of the 50-strong creative department and appointing new talent.
Since then, WCRS has landed a range of new clients including the Royal Air Force, Betfair, King Digital Entertainment, Notonthehighstreet.com and B&Q.
The agency has also scooped creative awards including Best Use of New Technology in Digital Craft at Creative Circle in 2013 for Women’s Aid "blind eye" and a silver at the 2013 Campaign Big Awards for Warburtons "half and half".
Matt Edwards, the chief executive of WCRS, said: "Billy and Ross have done everything Leon and I asked of them and more.
"They have built a creative department of big-idea generators, designers and technologists, and our work is cutting through and getting talked about. They have an ambitious plan for our creative output over the coming months and we’re looking forward to working with them to make it happen."
Faithfull and Neil have been a creative team since 2001. They started their advertising careers at Mother before joining HHCL.
In 2005, the pair moved to WCRS, where they have worked on accounts including Santander, the Royal Marines, Warburtons and B&Q.