Moseley joins Mother after six years at TBWA, where he worked with his partner, Graham Cappi, across a variety of the agency's accounts. Cappi will remain at TBWA.
While at TBWA Moseley worked on the agency's Sony PlayStation and Strongbow business, creating the spot featuring Jerry Hall alongside Johnny Vaughan.
He also worked on the Labour Party account, creating the poster that spoofed the action movie genre in the run-up to the election. The ad won a silver at last year's APG Creative Planning Awards. Moseley also wrote the 1999 Equitable Life ad with Muhammad Ali.
Moseley said: "It's such an exciting opportunity to work with Robert again, and at Mother. All of its work seems to be good - there doesn't seem to be a duff account. It seems to have a vision that works for everything."