Carter joins the agency as an associate director in the public affairs and corp comms team, having worked as an account director in MS&L's corporate and planning division.
Joining F-H's 22-strong public affairs and corp comms team in February, he will report to the division's head Nick Williams.
Williams commented: 'Fleishman-Hillard is committed to growing its PACorp team, meaning we will be investing in more top-level people in the coming months.'
During his two-and-a-half years at MS&L, Carter worked with clients including Coca-Cola Europe, P&G and Rolex.
Prior to this he worked for more than three years at ReputationInc.