In a ceremony on Saturday, the council conferred the honour on 152 (Ulster) Transport Regiment Royal Logistic Corps and 152 Royal Electrical and Mechanical Engineers Workshops.
Some of the members who marched through the streets of Castlereagh at the weekend have returned from service in Afghanistan.
The 152 regiment has strong links with Castlereagh, and Lieutenant Colonel Burgess said they were delighted to receive the freedom.
He explained: "It's not something that happens very often, it's a fairly unique experience and our guys and girls, as volunteer reservists in the Territorial Army, join the Territorial Army to serve their country where they can.
He added: "Many of the people on parade have recently returned from operations in Afghanistan and this is one way that their really delighted to say the community recognising that commitment that the armed forces has to society here."
We are clearly very much part of the community and it's really humbling that one of the boroughs here has felt able to bestow a really great honour on us.
Lieutenant Colonel Burgess
First Minister Peter Robinson was among those at the ceremony paying tribute to the work done by the troops. He said it was especially poignant following the death of Drummer Lee Rigby, who was murdered in London on Wednesday.
"I've been out in Afghanistan, I've seen the job that these people do and they do deserve much more than the recognition that we can give them.
He added: "These men are heroes and they stand in our place in theatres of war, and when they come back they might expect to have some peace and stability and enjoy life.
"Yet they face ever present threat and the dreadful events of the last week in London draw to our attention the fact that these men are always on duty and always serving."
The regiment was presented with a certificate formally acknowledging their status as Freeman of the Borough, and given specially commissioned medallions.
Mayor of Castlereagh, Alderman Michael Henderson MBE, said they were delighted to publicly recognise the regiment's achievements of supporting the regular army.
"These are people who work during the day in normal jobs, give that up and then go out and help defend our country and also support our security forces.
He explained: "This is something they give up their time to do and their family time as well. They can be away for six months at a time."