Nucleus is charged with revamping the site around the latest content management system.
P&O Cruises new media manager Elliott Pritchard said Nucleus had been chosen Nucleus for its industry experience and technical insight.
Peter Matthews, Nucleus’ managing director, said “We are delighted to be appointed by P&O Cruises, one of the world’s great cruise brands, and look forward to a long and successful partnership.
"Our plans for the P&O Cruises website will set new standards for cruise websites.”
Nucleus previously worked on a website for Ocean Village – a sister-brand to P&O Cruises.
Elliott Pritchard, new media manager at P&O Cruises, added: "Nucleus impressed us with their understanding of our requirements, their technical insights, travel industry experience and highly professional approach."