The shop triumphed in a pitch against VCCP Blue and Isobel to handle the estimated £6 million account.
JWT is the global incumbent on the business with the account run out of its New York office. Royal Caribbean had previously adapted its international campaigns to run in the UK market, but the appointment of JWT London marks the first time that it will run work specifically targeting a UK audience.
The cruise ship market has recently been hit by the sinking of the Costa Concordia, which resulted in the deaths of several passengers.
James Whitehead, the executive partner of JWT London, commented: "We're very pleased to be partnering Royal Caribbean in the UK and it's going to be a challenging year ahead."
The media account, at AMS, is not affected by the review.