Although on the BMT Brighton Line, Seventh Avenue was built almost fifty years after the main segment of the line from
Prospect Park to
Brighton Beach opened in 1878. Prior to its opening, trains on the line used what is now the
Franklin Avenue Shuttle and a connection to the elevated
BMT Fulton Street Line on their way to the line's terminus at Fulton Ferry in Brooklyn or
Park Row in Manhattan.
Construction and opening Q train boarding at the southbound platform|left The
Dual Contracts were formalized in March 1913, specifying new lines or expansions to be built by the
Interborough Rapid Transit Company (IRT) and the
Brooklyn Rapid Transit Company (BRT; after 1923, the
Brooklyn–Manhattan Transit Corporation or BMT). Two lines under Flatbush Avenue, one operated by the BRT and IRT, were approved. The BRT route, an extension of the
Brighton Line, was to run under Flatbush Avenue and St. Felix Street in Downtown Brooklyn, with a station at Seventh Avenue. The IRT was authorized to extend its Brooklyn line (now the
Eastern Parkway Line) under Flatbush Avenue, with a four-track route paralleling the BRT's subway southeast of the existing
Atlantic Avenue station. Groundbreaking for the lines under Flatbush Avenue took place in May 1914, by which point the BRT line was reduced to two tracks. The Seventh Avenue station was built as part of section 1A of the Flatbush Avenue tunnel, which extended from Prospect Place to
Grand Army Plaza. The contract for this section was awarded to the Cranford Construction Company on May 1, 1914. The BRT Brighton Line's Seventh Avenue station opened on August 1, 1920, This moved trains from the elevated Franklin Avenue Line to the new underground line. ==Station layout==