The Classical Revival building was constructed in 1909-10 by local real estate developer Harry Wardman and Albert H. Beers.

The variety of building types and styles, and the unusual spatial configuration of the short blocks and irregularly-shaped lots, creates a richness of streetscape seldom found so intact in the city today.

The Northumberland stands in its original state; this unaltered condition contributes significantly to the building's importance.

The building is red and white brick and dressed limestone and features an eclectic collection of classical architectural elements.

The rectangular windows are unusually large and are capped by pressed brick jack arches with stone console keystones.

[clarification needed] An elaborate metal bracketed cornice forms a projecting cap for the building and eloquently defines the roofline.

Eclectic in design and decoration, it reflects the taste in vogue in New York City luxury apartments at the turn of the 20th century.

Facing the entrance at the first landing are three original curved stained glass windows with heraldic monograms (the initial N).

Each is headed by a finial in the form of an obelisk 5 feet 7 inches (1.70 m) tall, containing six marble steps, and six unusually shaped balusters.

The lobby of the Northumberland is distinguished by a wealth of decorative ornamentation associated with European architectural embellishments derived from classical, medieval, gothic, and renaissance motifs.

The marbleized walls, columns, side staircases, and fireplaces provide an elegant background for the ornamentation.