The appointment follows a competitive pitch called by ACS comms manager James Lowman in April (PRWeek, 12 April).
The AS Biss team, which replaces five-year incumbent Praxis, is headed by senior consultant Clare Cox, and reports to Lowman.
The brief involves all PA work, including monitoring, lobbying and strategic advice.
A key campaign for the agency, according to Cox, will be to continue ACS's work on the climate change levy, which taxes small businesses on their use of energy.
Compensation based on National Insurance contribution discounts is offered but many stores miss out as they employ a large number of part-time staff, whose wages fall below the NI contributions threshold.
ACS members include Londis, Spar and Ginsters.