Originally known as the Germania Life Insurance Company Building, it was designed by Albert D'Oench and Joseph W. Yost and built in 1911 in the Beaux-Arts style.

[4] The building is one of the few remaining major insurance company "home office" structures in New York City.

[4] According to critic A. C. David, the optimal building design included high ceilings and large windows to maximize natural light coverage.

[10] The Germania Life Building not only included these features, but also had a corner location that was conducive toward the maximization of natural light.

[12] The facades of the fourth through fifteenth floors are largely uniform, with shallow belt courses and quoins in the spaces between each set of windows.

Shallow balconies on the fourth floor, with stone colonnades, are located above the denticulated third-floor cornices on the Park Avenue South and 17th Street sides, and run across nearly the entire width of both facades.

[12][13] The beige-brick-clad north facade contains the recessed "light court" and is divided into two asymmetric sections, both with simple window openings.

[14][5] The center bays on the west and south facades contain projecting windowsills on the fourth through fourteenth floors.

[13] The W New York Union Square building's most prominent feature is its four-story mansard roof, which contains dormer windows, escutcheons, and five decorative keystones with garlands.

[15][16]: 22  Inspiration also came from the now-demolished New York Tribune Building (completed 1905) in Civic Center, Manhattan, which was topped by a three-story mansard roof.

The ground-floor entrance area also contains white English veined marble on the walls, capped by stucco decoration.

The restrooms are designed with hexagonal-tiled floors, tile wainscoting, and stalls made with marble barriers.

Directly to the south, accessed through three sets of openings,[14] is a 66-by-35-foot (20 by 11 m), double-height space, originally used for selling insurance before being converted into the W Hotel ballroom.

[37][38] The Nassau Street building had suffered from structural problems, the most serious being a sinking foundation,[39] and it was sold to the Fourth National Bank of New York in March 1909.

[37][40] The company also could no longer rent out its vacant space at Nassau Street at a profit, and its directors sought to build a new headquarters in advance of its 50th anniversary.

According to architectural writer Kenneth Gibbs, these buildings allowed each individual company to instill "not only its name but also a favorable impression of its operations" in the general public.

[19][43] Furthermore, life insurance companies of the late 19th and early 20th centuries generally built massive buildings to fit their large clerical and records-keeping staff.

[45] Sites in White Plains and New Rochelle in Westchester were considered, but both proposals faced opposition from residents and Guardian Life employees, leading the company to decide to expand its Union Square location.

Guardian signed a lease for 23,000 square feet (2,100 m2) in a fourth building, 215 Park Avenue South, in the early 1990s.

[50] As part of the conversion, Related planned to remove the red neon "Guardian Life Insurance Company" sign and replace it with "W New York Union Square", the name of the W Hotels resort that would occupy the building.

[22] The basement was used by several event spaces,[54] including Rande Gerber's Underbar lounge and Todd English's Olives restaurant.

[28] The W New York Union Square was sold in 2006 for $285 million to Istithmar World, a Dubai government-owned investment group.

[54] Marriott Hotels & Resorts purchased the W New York Union Square in October 2019 for $206 million, with plans to renovate the building.

[22][56][57] The next year, the LPC reviewed a proposal for a seasonal rooftop garden, designed by Beyer Blinder Belle.

[52] The modifications included decorative details such as glass-block walls and carpeted staircases,[59] as well as a retheming of the guest rooms.

[2] The W New York Union Square building was added to the National Register of Historic Places (NRHP) on May 25, 2001.