Outside will work with the SPA on a nine-month retainer to provide communications planning, media advice and reputation management. It is the first time the SPA has appointed a PR agency.
The SPA reviews cases referred to it by the Service Police or Chain of Command and prosecutes cases at Court Martial or Service Civilian Court.
The account will be led by Nick Caley, Outside’s head of corporate communications.
Alan Edwards, CEO of Outside, said: "The SPA carry out extremely important work and we are proud to be advising on their communications strategy."