Band & Brown, which already handles PR for Somerfield sister chain Kwik Save, replaces Clarion Communications.
Three-year incumbent Clarion was one of four agencies to be shortlisted in the scrap for the contract (PRWeek, 15 October).
Immediate PR priorities for Somerfield are promoting its presence at the upcoming BBC Good Food Show and the conversion of the 114 Safeway shops it acquired from Morrisons last month to Somerfield outlets.
Band & Brown will, however, not start work on the account until January.