[6] A short portion of the line, coming off the north side of the Manhattan Bridge through Canal Street to 14th Street–Union Square, opened on September 4, 1917, at 2 P.M., with an eight car train carrying members of the Public Service Commission, representatives of the city government and officials of the BRT, leaving Union Square toward Coney Island.

Service opened to the general public at 8 P.M., with trains leaving Union Square and Coney Island simultaneously.

[9][10] On August 1, 1920, the Montague Street Tunnel opened, extending local service from Lower Manhattan to DeKalb Avenue in Downtown Brooklyn by traveling under the East River.

On January 3, 1999, a schizophrenic man, Andrew Goldstein, pushed 32-year-old journalist and photographer Kendra Webdale onto the tracks from the Brooklyn-bound platform of this station.

[18] After two mistrials due to his mental incapacity, Goldstein pleaded guilty of manslaughter in October 2006 and sentenced to 23 years in prison.

[19] The incident led to the passing of Kendra's Law, which allows judges to order people suffering from certain psychological disorders to undergo regular treatment.

The platform walls feature mosaics depicting hats that famous people of the Flatiron District wore, including Oscar Wilde, Sarah Bernhardt, and W. E. B.

The Queens-bound platform has a bank of regular and high exit-only turnstiles, the station's full-time token booth, and four street stairs.

The Brooklyn-bound platform has a bank of regular and high exit-only turnstiles, a now defunct customer assistance booth, and two street stairs.

The one on the Queens-bound platform is unstaffed, containing High Entry-Exit Turnstiles and one staircase going up to the northeastern corner of 22nd Street and Broadway.