The original Royal Princess was christened by the late Princess Diana, who would have been Middleton's mother-in-law.
The christening for the $735-million ship took place Thursday in a live broadcast ceremony with performances from the Royal Marines Band, the Irish Guard bagpipers and Natasha Bedingfield. With the ceremony, the duchess becomes the ship's godmother.
The ceremony was also streamed online on the Princess Cruises website.
Middleton wore a dalmatian-print dress from London brand Hobbs that has since sold out.
“I name this ship the Royal Princess,” Middleton said. “May God bless her and all who sail in her.” These were the words Princess Diana used during the naming ceremony for the original Royal Princess in 1984.
To make the christening official, a $1,600 bottle of Moet et Chandon Champagne was crashed against the ship. The Nebuchadnezzar, as this particular size of bottle is called, contains the equivalent of 20 standard-sized bottles of champagne.
Middleton's due date is rumored to be July 13, and she is not expected to make any public appearances until the birth of the child. The christening sparked a frenzy on Twitter with trending hashtag #RoyalPrincess, leading some users to believe the future royal had been born.
Prince William and his bride are unlikely to take another public tour until 2014, after the baby has been born and Middleton has had a chance to spend time at home with the child.