Golley Slater is also understood to be handling media planning and buying for the brand. The Sun Maid media account was previously held by Mediaedge:cia.
The appointment will see Golley Slater adapt US-created work for the UK market. The advertising will stress a healthy "real fruit" message, reminding consumers that the raisins are made simply from grapes and sunshine.
Executions will target mothers in women's weekly and monthly titles, and will focus on the Sun Maid snack range, which also includes prunes and dried apricots.
Earlier this year, Sun Maid changed tack in its US TV advertising, bringing the iconic Sun Maid girl off its packaging and on to the screen as an animated brand spokeswoman to celebrate her 90th birthday.
The $7 million campaign was created by Duncan/Channon advertising in California, and features the Sun Maid girl doing yoga on the beach.
Previous UK advertising for the Sun Maid brand focused on Sun Maid fruit buns, a brand-licensed product made by Allied Bakeries. However, the product has now been discontinued.
Golley Slater was unavailable for comment.
Last month, Golley Slater acquired McCann Erickson Leeds for an undisclosed sum. The purchase was the latest investment by the group. Golley Slater bought Push Digital in February and the Edinburgh-based agency Talented in September 2005.