Synopsis founder and managing director Bill Quirke will run the account, reporting to head of development and communication John Morris.
Morris said the hiring of Synopsis marked the first time Debenhams, which employs more than 22,000 staff, had retained internal comms specialists.
The brief is to reinforce the chain's Four Values, outlined when CEO Belinda Earl took charge 18 months ago. These values are: being 'passionate about the customer'; using a 'one-team' approach; acting on the basis of 'trust and accountability'; and 'innovating'.
'We hope to use the internal comms function to engage employees behind that brand promise,' Morris said.
'Internal comms is part of our strategic development and can help drive profitable growth. We also want to improve the level of communication between stores and head office,' he added.
While internal comms is a new function within Debenhams, the placing of a senior manager such as Morris in charge of it signifies the attention the group was paying to that area, a spokesman said.
Although Morris reports through the group HR function, he is expected to work closely on the Four Values project with head of PR Catherine Sturgess and head of IR Joanna Lane-Jones. The latter two use Jackie Cooper PR and The Maitland Consultancy for outside advice on their respective remits.