Dale Gall, EMEA chief executive at MullenLowe Profero, will take over the role that Warren left in May. He will report to Alex Leikikh, global chief executive at MullenLowe Group.
The move sees just one UK CEO for the group, which is aiming to create a more streamlined agency.
Charlie Hurrell, managing director at MullenLowe London, and Buster Dover, managing director at Profero, will expand their remits to oversee day-to-day operations of the London agencies.
Jonathan Fowles will continue running Mediahub, and Open’s global chief executive Anthony Hopper will continue in his role.
Elliott joined the agency 11 years ago as client services director when the shop was known as DLKW. He moved up the ranks, becoming deputy managing director in 2008, managing director in 2012 and finally chief executive last year.
Gall joined Profero in 2009 as global strategy director, and became the EMEA chief executive in 2011. His career spans VCCP, J Walter Thompson and WCRS.
Profero launched in 1998 and was acquired by Lowe and Partners in 2012.
Holding company Interpublic Group merged Mullen Advertising with Lowe and Partners last year, and rebranded as MullenLowe Group in January this year.
Leikikh said: "At MullenLowe Group we are building a new type of network.
"A network not defined by silos, but with integrated communications planning built into the model. A network where we bring together the best cross section of our talent across all disciplines to work on client business challenges and drive more creativity from day one.
"Dale is uniquely placed to lead our hyperbundled offering in the UK given his proven track record of multi-channel success spanning a 20-year career in advertising, media and technology."
Richard Warren’s departure left Tom Knox as the sole remaining founder of DLKW.
Knox dismissed claims that the latest move is about cost-cutting and explained it as the next step in "hyperbundling".
He told Campaign: "We’ve been talking about bringing all of our services together in a more together way. Step one was moving everyone into one building and what we are looking at now is a structural change with one CEO and with us working as one team.
"We can still pitch as separate businesses but we want to talk to clients as one group [with a number of different offerings]."