The move marks the second phase in an internal comms revamp, led by head of internal comms Ghassan Karian.
Rolls-Royce's in-house team last year implemented a review of internal comms at a corporate level. Some changes were made following the results, including the relaunch of the employee magazine Rolls-Royce World, now titled The Post.
On the business unit audit, Karian said: 'The aim is to improve communication in a way that is more actively focused on each business unit.'
FH won the business after a competitive pitch against Synopsis Communications Consultants, MCA Banner McBride, Bell Pottinger and Smythe Doward Lambert.
FH director and head of internal comms Nicholas Wright heads the brief.