The move, which reunites him with Nick Bell, the JWT executive creative director, brings the curtain down on Carty's 12-year spell at AMV.
Carty will continue to direct through Gorgeous Enterprises, the production company he signed up to two years ago after swapping his contract at AMV's creative department for a more freelance role.
Bell said: "Tom has produced some fantastic work over the years and I know he loves advertising. We worked together for some time at AMV and I took the opportunity to harness his talent while it was available."
Carty started his career at Dorland Advertising before moving to TBWA\London, where he and Walter Campbell were a creative team.
While at AMV, Carty and Campbell created Guinness' "surfer" TV spot.
The 60-second black-and-white ad was later selected by the Design Council as one of the ads of the millennium for its use of state-of-the-art technology.
Carty also directed the "rush hour" ad for BBC1, featuring a man leaping across London rooftops.
Carty said: "I think Nick is going to make JWT a great creative resource and it will be nice to be there at the beginning as part of it."