Calacus has been appointed by ForceSelect for its national launch this month.
ForceSelect is run by former army officers Hugh Andree and Lucy Wood, along with former SAS hero and bestselling author Andy McNab, and former army chief of staff general Sir Michael Jackson.
ForceSelect will provide support and mentoring for service leavers as they adjust to civilian life. It will also work with a wide range of large and small companies to provide job opportunities for candidates.
UPS has already signed up as a ForceSelect partner and the organisation has been endorsed by the Ministry of Defence.
ForceSelect founder Andree said: 'There is a huge opportunity for British business to tap into the skills and experience that service personnel can offer and it is our objective to provide these men and women with the best and most appropriate career opportunities available.'
Led by David Alexander, Calacus will provide media relations support for the launch and provide ongoing PR advice as the company expands across the UK.
Calacus was established in 2007 by Alexander, who previously worked at Hill and Knowlton, Porter Novelli and Weber Shandwick.
Current clients include the British Sport Museum and government-appointed research charity Ricability.