The move sees Webb return to the UK after a year in Australia, where he worked at Publicis Mojo. He will partner McCann's executive head of art, Mark Reddy with whom he worked at DDB London.
Webb joined DDB in 1989. He worked on PG Tips and Courage and was part of the team that developed the "no-nonsense" campaign for John Smith's bitter.
Campbell said: "Good writers are hard to find and Dean is bloody excellent."
Webb will also work with designer Dingus Hussey, who joins from DDB.
Hussey worked for three years with Reddy at DDB on accounts including Volkswagen.
