P&O Cruises' contract with Weber Shandwick will terminate at the end of this month, when Griffiths will start work as PR manager, a newly created role.
P&O Cruises head of brand marketing Michael Bedingfield, to whom Griffiths will report, said: 'We have decided to bring PR in-house to give more prominence to PR in our marketing mix.'
Bedingfield added that a recruitment process was underway to hire two more press office staff.
Griffiths starts work at Southampton-based P&O Cruises from 2 December, with her primary aim being to set up a press office and to devise PR campaigns.
It is understood that the company is aiming to target PR campaigns towards those holidaymakers who would not usually consider cruise holidays.
Earlier this month, P&O Cruises' new vessel, the Oceana, set sail from Florida on its maiden voyage after an extensive refit. It will spend the next few months cruising the Caribbean.
In May next year, P&O Cruises will launch its fourth vessel, Adonia, from Southampton.
One of Griffiths' initial tasks will be to organise PR activity surrounding a naming ceremony for both the Oceana and Adonia in May.
Bedingfield confirmed the increase in capacity of the two new ships will mean that 'PR and advertising will be scaled up'.
Griffiths joined BGB from the former McCluskey & Associates, now McCluskey International, seven years ago as a senior account executive.
At BGB, Griffiths worked on accounts including UK cruise industry trade body the Passenger Shipping Association.
