Built during the Second Settlement the complex contains a central soldiers' barrack with officers' quarters on either side.

Other buildings around the barracks contained kitchens, washhouses, privies, a military hospital, guard room, powder magazine and a well. Surrounding the complex is a high wall with corner turrets. During the Third Settlement the Old Military Barracks were used to house the island's first Methodist Church, and today they are used as the chambers of the Norfolk Island Legislative Assembly.