Designed by architect Kevin Roche of the firm Roche-Dinkeloo and opened in 1976, the hotel is located at 44th Street and First Avenue, near the headquarters of the United Nations.

It occupies part of the ground floor and top 13 stories of One and Two United Nations Plaza, a pair of 39-story skyscrapers also designed by Roche-Dinkeloo.

The ground story contains the lobby, which consists of a reception area, foyer, and ramp with mirrored surfaces and polygonal lamps.

[17][c] To comply with zoning regulations, the northern facade contains two setbacks sloped at a 45-degree angle, while the southeast corner has a cutback on its lowest 12 stories.

[4][9] Paul Goldberger called One United Nations Plaza "one of the finest postwar skyscrapers in the city",[18] while John Tauranac said the building "shimmers in the sun" as seen from a distance.

[23] According to architectural writer Eeva-Liisa Pelkonen, the two buildings formed a "kaleidoscope, always changing, always moving [...] a destination and an active participant in the disco era of the late 1970s and the 1980s".

[33][34] The restaurant is sunken slightly below ground level[34][35] and occupies an irregularly shaped space at the northern end of the hotel.

[34] The Ambassador Grill became a popular meeting spot for United Nations diplomats after it opened in 1975,[36][37] and it retained this status throughout the years.

[27][34] The floor contains a twisting path with dark green and white marble tiles,[2][42] which runs from the entrance to the dining areas.

[2][42] The ceiling above the main pathway includes rectangular glass panels, held in place by metal slats; Ada Louise Huxtable compared it to the roof of a greenhouse.

[54] Mae Festa, an interior designer working in Roche-Dinkeloo's office, had acquired the tapestries from various antique stores and flea markets worldwide.

[9] By 1966, the headquarters of the United Nations was overcrowded, leading US and UN officials and the Ford Foundation to develop plans for new office space, hotels, and apartments nearby.

[64][65] Roche-Dinkeloo released revised plans in November 1969, which called for a 700-room hotel and three connected office buildings with 3×10^6 sq ft (280,000 m2) of space.

As part of the training process, several high-ranking staff members simulated "finicky guests" for a week before the hotel opened.

[69] In 1980, to accommodate increasing demand for office space near the UN headquarters, the UNDC started constructing Two United Nations Plaza on 44th Street.

[78] The staff maintained a "General Assembly Manual" in which they recorded diplomats' preferences, including diagrams of furniture layouts for delegates who visited multiple times.

[83] The administration of mayor Rudolph W. Giuliani announced in May 1993 that it would sell the hotel[56] in an attempt to reduce the city government's budget.

[83] Hong Kong hotelier Regal Hotels International agreed in May to buy the property for $102 million, and the sale was finalized that July.

[98] About a quarter of the hotel's profit was directly related to business at the United Nations, and nightly room rates were typically raised during General Assembly meetings.

[102] The first phase, which cost $30 million and was completed that September, entailed converting the rooms in Two UN Plaza into a luxury wing called the "West Tower".

[105][106] Preservationists expressed concern that the renovations would result in the destruction of the public interior spaces,[44][107] as the hotel operator had indicated its plan to redesign the Ambassador Grill.

"[18] Ada Louise Huxtable said the United Nations Plaza Hotel's design features, such as its angled geometry and "luxurious and tasteful simplicity", collectively created a "rich, visual intricacy".

[43] Angela Taylor wrote for The New York Times that "the best things about the new United Nations Plaza Hotel are what it doesn't have", which included "canned music", a crowded ballroom, or paper tents for advertising.

[27] William Marlin of The Christian Science Monitor wrote that, despite the hotel's relatively low construction budget, "one can only be amazed at [the rooms'] quality and absorbing delight".

[53] In 1979, the New York City Club presented the United Nations Plaza Hotel with its Albert S. Bard Award for "excellence in building design".

[117] Two years later, Clara Hemphill wrote for Newsday that, while the mirrored public spaces were "not a study in quiet good taste", the UN Plaza was "a comfortable hotel with great views" because of how high it was.

[97] The Journal of the American Institute of Architects wrote that "the sense of firm conviction about design so evident in the towers' exteriors seems somewhat shaken once one comes in from outdoors",[29] and Robert A. M. Stern called the lobby "garish".

[4][19] In 2024, a writer for The Telegraph praised the views from the room; the fact that the site was relatively quiet but still near multiple points of interest; the large units; and the "scores of marble, mirrored surfaces and space galore".

[119] After foods from Gascony were added to the menu in 1986, Bryan Miller wrote for the Times: "Several of the Gascon dishes alone make a trip to the Ambassador Grill worthwhile.

[120] Sheraton said the ceiling was "startling and somewhat wonderful" in spite of the quality of the food,[36][119] while Miller said: "The subterranean dining room is striking with its interplay of dark walls, smoky glass panels and starry lighting.