The structure is named for Philip A. Hart (1912-1976), who served 18 years as a United States Senator from Michigan.

However, due to the resource and financial demands of the Korean War, the building was scaled back and occupied only the western half of this area.

[4] In April 1973, the Architect of the Capitol awarded the architectural design contract to John Carl Warnecke, a nationally prominent architect working in the District of Columbia who had helped save Lafayette Square and designed the John F. Kennedy grave site.

[9] The poor and uneven condition of the soil at the site caused delays in the excavation, and major cost increases.

[7] Architect of the Capitol George M. White argued the construction cost was a reasonable $110 per square foot.

[17] To save costs, the building gave each person a cubicle, rather than an office, which greatly upset Senate staff.

[19] In late 1982, the Senate found $9.5 million ($29,993,793 in 2023 dollars) in unused funds, which it designated to pay for the modular furniture and partitions for use in the Hart building.

[8] To echo the courtyards of Dirksen and Russell, the Hart building has an atrium covered by a vast skylight.

[21] The walls of the interior of the structure, including the atrium, are clad in the same white Vermont marble as the exterior.

[8][22] Due to the building's layout, a workspace with identical ceilings and views is adjacent to each senator's office.

These partitions were originally purchased for only a handful of offices, due to cutbacks in the building's furnishing budget.

[7] The interior elevator doors were also cast in bronze,[7] and areas in the floors in suites, meeting rooms, and some public areas had removable panels and built-in tubing which allowed for the easy replacement or upgrading of electrical, telecommunications, and computer wiring.

These allowed certain items to be restored, such as the large hearing room, auxiliary area carpeting, vertical blinds,[8][15] and the gymnasium equipment (now estimated to cost just $736,000 ($2,323,730 in 2023 dollars)).

[14] The building's design deliberately spared the adjacent Sewall–Belmont house, a historic structure that serves as headquarters for the National Woman's Party and a museum about the women's suffrage movement.

[24] Located on the second floor of the Hart Senate Office Building, the two-story high room[23][25] has studio-quality television lighting built into the ceiling.

[27] Privately, members of Congress, their staff, and often witnesses access the hearing room from nondescript doors on the second floor of the Dirksen Senate Office Building.

[28] In 1989, the Senate approved a plan to upgrade the subway beneath the Hart and Dirksen office buildings.

[30] The atrium in the Hart Senate Office Building is 90 feet (27 m) high[31] and capped by a lighting system and skylight.

The upper part of the work consists of a mobile, "Clouds", made from curved aluminum plates suspended from the roof on a shaft.

[36][40] The lower part of the work consists of a stabile made of four flat, triangular-shaped steel plates painted matte black and supported by two curving legs.

White gave his approval for the full-size work to be installed at the Hart Senate Office Building.

[10][20][35][37][41] During the budget battles in 1979 over the cost of the Hart Senate Office Building, funds for completion of the Calder work were deleted.

The foundation's goal was to raise funds for the placement of art through the United States Capitol Complex.

[37] Some time after the installation of the work, the motor malfunctioned and the mobile portion of Mountains and Clouds stopped rotating.

[42] "He had mounted the forms atop one another before, but had never used them separately in a single piece as he anticipated to do with moving clouds and stationary mountains," says Capitol Hill reporter Justin Cox.