The pair will work on R/GA’s global Unilever business and support the agency in new-business pitches.
After leaving Critical Mass – where they were part of the European leadership team – last year, Williams and Roberts freelanced at agencies including AKQA Amsterdam, Momentum Worldwide and DigitasLBi.
At Critical Mass, Roberts led creative teams producing work for brands including Adidas, Nissan and Procter & Gamble.
Williams managed a team of experience designers at Critical Mass and was responsible for hiring, mentoring and raising the standards of that discipline.
George Prest, R/GA London’s vice-president and executive creative director, said: "These hires are part of an exciting new creative approach, marking a shift into a more holistic approach to brand-building. This strategy requires a new breed of creative leaders – hybrids who are comfortable working in a media-agnostic way."