Staff Sergeant is the sixth enlisted rank of the UNSC Marine Corps and the UNSC Army (E-6), and the fifth enlisted rank in the UNSC Air Force (E-5). It is a staff non-commissioned officer rank. The rank insignia is represented by three gold "chevrons" over one "rocker" in the Army, three red chevrons and one rocker with crossed rifles in the middle field for the Marines, and four white rockers for the Air Force.
Army and Marine Staff Sergeants are equal to a Technical Sergeant in the Air Force or a Petty Officer First Class in the Navy. Air Force SSgts are equal to a Sergeant in the Army and Marines, and a Petty Officer Second Class in the Navy.
Staff Sergeants typically command squads of 9 - 11 Army Infantry and serve as Platoon Sergeants in the Marines, which are the second in command of the platoon. Avery Johnson and Nolan Byrne were platoon leaders on Harvest, and were tasked with training a Colonial Militia, with each responsible for a platoon-sized group of men. Although a bit different from the other services, it is the Air Force's first non-commissioned officer rank as well as the first rank to which promotion is on a competitive basis.
- Compared to other services, the rank of SSgt. in the Air Force is relatively low despite being a position given to flight sergeants.
- The most notable Staff Sergeant was Avery Johnson, who first saw action against the Covenant Empire at Harvest. He died during the Raid on Installation 04B.