Booth and Flinn was awarded the first contract for the line, namely a tunnel under the East River, in January 1916.[7] At the time, the Public Service Commission was completing plans for the rest of the line;[8] the commission began accepting bids for two parts of the line within Manhattan, sections 1 and 2. in April 1916.[9] The next month, Booth and Flinn won the contract for section 1, which was to cost $2.528 million (equivalent to $70.784 million in 2023).[10] By early 1919, the section of the line under 14th Street was about 20 percent completed.[11]
In 1922, the Charles H. Brown & Son Corporation was contracted to build out the Canarsie Line's stations in Manhattan, including the First Avenue station.[12] Track-laying in the tunnels between Sixth and Montrose Avenues started in the last week of October 1922.[13][14] The First Avenue station at Union Square opened on June 30, 1924, as part of the 14th Street–Eastern Line, which ran from Sixth Avenue under the East River and through Williamsburg to Montrose and Bushwick Avenues.[15][16]
The station originally had entrances only at its western end, on First Avenue. Its eastern entrances at Avenue A were built as part of the wide scope in the 2019–2020 rebuilding of the Canarsie Tubes that were damaged during Hurricane Sandy, and to improve service for people living in Stuyvesant Town–Peter Cooper Village, the East Village, and Alphabet City. Work on the entrances began in July 2017,[18][19] necessitating the relocation of bus stops at that intersection.[20] The entrances to the Brooklyn-bound platform were opened on November 4, 2019. The entrance to the Eighth Avenue-bound platform was expected to be opened by the end of 2019,[21][22] but the opening date was postponed to February 10, 2020. This was followed by the temporary closure of the entrances at First Avenue.[23]
New elevators were built at the new eastern entrances[24][25] and were opened on August 6, 2020.[26] Substantial completion of the entrances was projected for November 2020.[27][28]
This underground station has two side platforms and two tracks. It is the easternmost Canarsie Line station in Manhattan. East of here, the line travels under the East River to Williamsburg, Brooklyn. The platforms are columnless and have the standard BMT style trim-line and name tablets. The former contains "1" tablets in standard intervals while the latter consists of "FIRST AVE" in white seriffed lettering.
Exits
The station's western entrances are at the (railroad north) end of the station; from each platform, a single staircase goes up to a small mezzanine that contains a turnstile bank, token booth. Two street stairs to the Eighth Avenue-bound platform lead to the northeastern corner of First Avenue and 14th Street, while the ones to the Brooklyn-bound platform lead to the southeastern corner. The mezzanine on the Brooklyn-bound side had a florist shop outside fare control; the shop closed in 2019. There is no free transfer between directions at this station.[29]
The station's eastern entrances are at the railroad south end of the station; there are platform-level turnstile banks from each platform. Two street stairs to the Eighth Avenue-bound platform lead to the northwestern corner of Avenue A and 14th Street, while two more to the Brooklyn-bound platform lead to the southwestern corner. Each eastern entrance has an elevator between the platform and the street.
Art
The station contains two sets of mosaic artwork by Katherine Bradford.[30][31] The eastern entrances include three large works collectively titled Queens of the Night, which depict figures in dancelike poses against a sapphire blue background. In addition, the First Avenue mezzanines contain two smaller works of flying superheroes, titled Superhero Responds.[31][32] The mosaics cover 400 square feet (37 m2) in total. When the artworks were commissioned, Bradford used the L train on her daily commute, passing through the First Avenue station.[30]
^"When Will Dual Subway Be Finished?: Completed Work Cost 188,332,000--unfinished Contracts Amount to 20,000,000 Two Bodies Responsible for Construction Lack Mutual Confidence and Team-work". New-York Tribune. January 5, 1919. p. D10. ISSN1941-0646. ProQuest575999620.
^"Pushing Throng Christens Spur Of B. M. T. Tube: Hylan Runs the First Train From Brooklyn to 14th Street, Then Assails "Interests'" at Luncheon Yearns to Boss System Transit Commission Heads Remind Mayor Epithets Won't Solve Problems". The New York Herald, New York Tribune. July 1, 1924. p. 12. ISSN1941-0646. ProQuest1112998377.
Note: Service variations, station closures, and reroutes are not reflected here. Stations with asterisks have no regular peak, reverse peak, or midday service on that route. See linked articles for more information.
Stations of the New York City Subway, by line (physical trackage)
Stations and line segments in italics are closed, demolished, or planned (temporary closures are marked with asterisks). Track connections to other lines' terminals are displayed in brackets. Struck through passenger track connections are closed or unused in regular service.
New York City Subway station (rapid transit)
(all times)
NYCT Bus: M14A/M14D Select Bus Service, M15 (northbound), M15 Select Bus Service (northbound)
ADA-accessible 
34.8%
