Tofield is joining in September from the Cabinet Office, where she was appointed in March to the newly created role of cross-government head of media relations. It is not yet clear if she will be replaced.
It is understood that Rae Stewart, who has been working as interim director of comms since the departure of Kim Worts in September last year, will continue to work for Defra, but his position in the department has not yet been confirmed.
Separately, new Environment Secretary Liz Truss has brought in Ruth Porter, head of economics and social policy at the think-tank Policy Exchange, as a media special adviser. She will be replaced at Policy Exchange by Steve Hughes.
Tofield was unavailable for comment.