In 1922, the Boston Elevated Railway opened a prepayment transfer station at Lechmere, separating the surface streetcars from the subway routes.

[2] Public artwork at the station includes Field Notes by Randall Thurston – a set of panels on the elevator shafts depicting birds and vines.

[11][9] The station was popular with employees from Somerville commuting to the factories of East Cambridge; among its more famous users was Benjamin Butler.

[12][13] The Fitchburg Railroad also had an East Cambridge station (primarily served by Lexington Branch trains) located at Linwood Street, just over the Somerville border, in the mid-19th century.

[17] Although most inner stations were largely replaced by streetcars and automobiles at this time, East Cambridge was still used by both industrial workers and by those headed to the Middlesex County Courthouse, and the proposed closure was locally opposed.

[18][19] The Public Utilities Commission approved the closure of East Cambridge and nearby Prospect Hill in March 1927; one train was rescheduled for ten minutes earlier to accommodate court attendees.

[29][25]: 7 [30] The incline at the north end of the viaduct, which connected to the surface streetcar tracks, occupied half the block between Lechmere Square and Second Street.

He proposed that the northern transfer station be at Lechmere Square, with elevated rapid transit platforms and surface loops for streetcars.

Streetcars then looped under the viaduct at Lechmere Square and picked up passengers using two tracks off Bridge Street, where a waiting room was located on the platform.

[42] On January 2, 1923, some off-peak trips were extended through the Boylston Street Subway to the surface station at Kenmore; all-day service began on October 10.

The outbound surface track used by Cambridge Street cars was rebuilt and set in concrete paving to accommodate buses.

[29] The practice of routing inbound buses through Lechmere Yard was ended in the late 1970s, likely when the Boeing LRVs (which were larger and heavier than previous streetcars) began operating on the Green Line.

The ramp, largely disused after heavy maintenance shops at Riverside opened in 1976, was removed in the late 1980s to make room for additional storage tracks.

[29] Around 2000, portable lifts were added at Lechmere as a temporary accessibility measure, along with a wooden mini-high platform on the inbound side.

[25]: 10  Green Line E branch service to Lechmere resumed on November 12, 2005, with buses returned to their previous routing at the station.

[80][81] Variations on this plan were proposed several times during the 1930s, including subway extensions from Haymarket or Bowdoin to replace the Lechmere Viaduct.

[82][83] In 1943, the state legislature appointed a commission headed by Arthur W. Coolidge to plan for the future of transit in the Boston region.

The 1945 and 1947 reports from the Coolidge Commission recommended nine suburban rapid transit extensions – most similar to the 1926 plan – along existing railroad lines.

[84][86] The 1962 North Terminal Area Study, claiming that the 1959 Highland Branch conversion showed that PCC streetcars were inadequate for suburban rapid transit service, recommended that the elevated Lechmere–North Station segment be abandoned.

[87][f] The 1966 Program for Mass Transportation, the MBTA's first long-range plan, listed an approximately 1-mile (1.6 km) extension from Lechmere to Washington Street as an immediate priority.

A second phase of the project would extend Green Line service from Washington Street to Mystic Valley Parkway (Route 16) or West Medford.

[80] Plans in 1978 for redevelopment of the Lechmere Canal area called for a new elevated station on the east side of the O'Brien Highway.

[96] In 1999, Guilford Transportation Industries (GTI) proposed to develop 50 acres (20 ha) of disused railroad yards on the east side of Lechmere Square.

[97][98] After a 2005 lawsuit by the city of Somerville and the CLF, the state began planning of the Green Line Extension (GLX), including a second branch from Lechmere to Union Square.

[104] Under draft plans released in 2008, the Urban Ring would have approached Lechmere Square from the north on a dedicated bridge over the MBTA Commuter Rail Maintenance Facility, continuing on Morgan Avenue and First Street.

[114] The City of Somerville, MassDOT, and the MBTA reached an agreement in August 2012 to open the Union Square Branch and Lechmere station by early 2017, with construction to begin in 2014.

[2] Early GLX work included the demolition of a disused MBTA facility at 21 Water Street to make room for the new Lechmere station.

Notice to proceed for the early work was issued to Barletta Heavy Division on January 31, 2013, and construction started in March.

[2] Work at Lechmere station started by September 2019; the concrete pillars for the viaduct were poured later that year, while installation of the beams supporting the trackways and platform began in January 2020.

The Green Line between Union Square and Government Center was closed from August 22 to September 18, 2022; the closure allowed for final integration of the Medford Branch, elimination of a speed restriction on the Lechmere Viaduct, and other work.