The accolade will be bestowed upon troops from 152 Ulster Transport Regiment and 152 Royal Electrical and Mechanical Engineers during a ceremony on Saturday.
It is the highest honour a local authority can grant.
"Over 300 members of the regiment have been deployed over the last 15 years to support operations in Iraq, Afghanistan and the United Nations in Cyprus," said Lieutenant Colonel Tim Burgess.
"The Freedom of the Borough is a great honour bestowed on the regiment which will be cherished by our members for years to come."
The soldiers, based in Holywood and Londonderry, served alongside the Regular Army in Afghanistan last year helping move supplies such as artillery ammunition and fuel.
It is expected they will return to Helmand province next year.
First Minister Peter Robinson will be amongst the dignitaries attending the freedom ceremony at Castlereagh Council civic centre.
Specially commissioned medals will also be presented to the service personnel on parade.