The Caucus Room in the Cannon House Office Building is an excellent example of the Beaux Arts style of architectural design. Grand, well ordered, and richly detailed, the room provides a dignified environment in which important political meetings and social functions are held. It is the oldest and one of the largest assembly rooms built for the House of Representatives outside the Capitol. Before the construction of the Cannon House Office Building, caucuses and other meetings took place in cramped committee rooms in the Capitol.

In 1903, the House Office Building Commission retained the services of John Carrére and Thomas Hastings, a prominent New York architectural partnership, to design a new office building for the House of Representatives. Their training at the Ecole des Beaux-Arts in Paris, which resulted in a thorough knowledge of classical architecture, is seen throughout the building and is particularly apparent in the Caucus Room. The room lies at the end of a progression of monumental spaces, which begin with the rotunda and continue in the marble staircases that land directly in front of the principal entrance to the Caucus Room. Through this architectural hierarchy, one is led from the building's "front door" directly and powerfully to the Caucus Room. Measuring 74 feet long by 54 feet wide, the room is treated with paired Corinthian pilasters standing on a continuous pedestal and supporting a richly detailed entablature including dentils, modillions, and egg-and-dart moldings. The rich ceiling is decorated with a variety of classical motifs: rosettes, guilloch, and Greek key. Six windows on the courtyard wall and four crystal chandeliers light the room. The three-tiered chandeliers, which are original to the room, feature etched globes.

This room is the site of numerous dinners, receptions, and other events each year; unlike its counterpart in the Russell Senate Office Building, this room hosts no prominent public hearings. Because permission to use the room is obtained only through the Speaker of the House, information on patrons is not always available. Some events of note that have taken place in the room date back at least to 1943, when 350 women were sworn in as members of the Women's Army Corps. More recently, the commencement ceremony for the last graduating class of Capitol pages was held in the room in 1983. (Since then, pages serve only during their junior year of high school.) In 1984, the Kennedy Center kicked off festivities for its seventh annual Honors Gala with a formal dinner in the Caucus Room. Annually, an informal luncheon is held to honor the winners of the "Artistic Discovery" high school art competition.