He takes up the responsibilites of Simon Clift, who is stepping down, and has added communications to the role.
Weed will take up his new role on 1 April 2010 and will be a member of the Unilever Executive, reporting to chief executive Paul Polman.
Clift announced he was stepping down last month.
Weed is a former executive chairman of Lever Faberge and senior vice president Unilever.
Weed has also held the position president of the Marketing Society.
Polman says “This is the first time Unilever has had a CMO at the toptable and is a key step to having a sharper consumer focus in the company. Keith will be leading marketing, including the development of the Unilever Brand and will also assume responsibility for the communications functions.”