The House Sergeant-at-Arms is Wilson Livingood, while Gregory Casey holds the position in the Senate. The Speaker of the House and the Senate Majority Leader have the prerogative of selecting and nominating an individual for the post in their respective chambers. Their candidate must then be elected by majority vote of the full chamber, but this is a mere formality.

The Sgt-at-Arms' primary responsibility is to maintain security for his chamber, buildings, and grounds. He sits on the board which governs the sizeable Capitol Hill Police Force and sets its policies. He directly controls access to the chamber by supervising the doorkeepers, and is responsible for maintaining order in the galleries and on the floor. The Sgt.-at-Arms greets and escorts VIP and foreign visitors to the Capitol, e.g. on State of the Union night. The House Sgt-at-Arms also has responsibility for transporting the bodies of deceased Members and making secure travel arrangements for Members attending funerals as an official delegation. The Senate Sergeant-at-Arms is given a broad range of administrative duties by his chamber. He supervises the operations of the Senate's Computer Center, telephone system, recording studio, post office, mass mail and printing services, barber and beauty shops.

In the House, the Sergeant-at-Arms has another function unique to that chamber. He is the keeper of the "Mace," the ebony and silver rod with a silver eagle on top, which represents the authority of the House. When the House convenes its daily session, it is the Sergeant-at-Arms, bearing the Mace, who escorts the Speaker into the chamber. When the House transforms into the Committee of the Whole for certain legislative proceedings, the Sergeant-at-Arms can be seen moving the Mace from the top tier of the rostrum, at the Speaker's right, to a less visible position on a lower tier. This signals the House is no longer meeting but is now sitting as a Committee. During its first 100 years, the House followed the practice of asking its Sergeant-at-Arms to quell disorder on the floor by parading around with the Mace. The sight of this symbol of order was supposed to be sufficient reminder to Members to resume parliamentary decorum.

In the Senate, the Sergeant-at-Arms had a moment in the media spotlight in 1988, when then Senate Majority Leader Robert Byrd (D-WV) made a motion on the Senate floor that Senators absent from the floor be arrested and brought to the chamber. The absentees were deliberately stalling the consideration of campaign finance legislation by preventing a quorum from being achieved. By vote of the Senate, the Sgt.-at-Arms was handed arrest warrants and instructed to find and escort the absentees to the chamber. Senator Robert Packwood (R-OR) was the first "captured," and forcibly brought to the floor by the Sgt.-at-Arms and several of his plainclothes men. Packwood's presence registered a quorum; no other Senators had to be sought.

The Senate has had one female Sergeant-at-Arms, Martha Pope, who served from 1991-1994, under Majority Leader George Mitchell. The House has never had a woman in the post. The first Sergeant-at-Arms in the House was Joseph Wheaton, elected in 1789. The Senate at first appointed only a doorkeeper in 1789, James Mathers, but changed his title to Sergeant-at-Arms in 1798.