Moss was formerly the creative director and a founding partner of the six-year-old Incline. Tim Hurles, Good Technology's creative director, left the agency several months ago.
"It made sense for me to take the role across the group," Moss said. "No-one has been found who brings the knowledge and experience I brought to the role."
In September, WPP announced it was to merge Incline - a subsidiary of Mediaedge:cia - and Good Technology. They will retain their individual brand names.
The companies are being co-located as part of what is interpreted as a cost-saving initiative.
The combined client list includes Sony, Audi, Selfridges, Direct Line and Sony PlayStation.
Both companies report to Good Technology's founder and managing director, Richard Davies, who has been promoted to chairman. Davies will report to Rob Norman, the chairman of Mediaedge:cia UK.
Norman has tasked Davies to seek out agencies for acquisition in WPP's first moves to increase its digital offering since the dotcom bust.
"We are looking at competent businesses that have perhaps lost their way in the downturn and are working on our first acquisition," Davies said.