Following a pitch it has brought in comms assistance for the launch of Anthem of the Seas – a 4,180-passenger ship focused on music and entertainment.
TVC's client services director James Myers suggested the ship formed part of Royal Caribbean's efforts to attract a wider range of customers.
"The brief is about reaching a new audience, and reaching people who would not normally consider cruising," he said.
As part of a six-figure contract, the agency will use music to evoke "holidays and good times" in an attempt to expand a market worth £2.5bn in the UK.
The project work will build up to the new ship sailing out from Southampton in April 2015, with couples and families among the key younger groups targeted.
"It's a growing market," Myers said, "but it's growing slowly, with a large amount of return cruisers.
"Reaching a new audience is seen as difficult, so we're trying to help dispel the myth that a cruise holiday may not be the coolest, most credible way to spend a holiday."
Royal Caribbean, which posted a net income of $378m (£233m) for Q3, will continue to work with Siren PR on a retained basis.