The pair have won Cannes gold and silver Lions as well as D&AD Pencils. Their best-known recent work was the "dangerous liaison" spot for Levi's.
Before BBH, Williamson worked for WCRS and HHCL & Partners. Wakelam had stints at D'Arcy and Leo Burnett.
Micah Walker, the Publicis Mojo creative director who was formerly at Fallon in London, said: "I admired their work while in London and we're genuinely excited to have them join us. They could have gone just about anywhere they wanted."