The Cavalier Building is the largest freestanding building inside the walls of the Halifax Citadel. The building served as a barracks for up to 200 men as well as a platform for artillery. Seven 32-pounder cannons were originally mounted on the third floor. If required, the shingled roof could be removed to allow cannons a free field of fire. If the enemy succeeded in getting inside the Citadel, the Cavalier Building, with its stout stone walls and oak doors, represented the last line of defence.

Today, the first floor of the Cavalier Building houses the Citadel's information centre, coffee shop, gift shop, a restored soldiers' library and a restored barrack room. The second floor is home to the Army Museum.