Since the beginning of 2016, the Friends of the South End Library (FOSEL) has been advocating at the city level for a five-phased renovation of the branch library in its current location. This is the second attempt by FOSEL to do so. The proposal calls for an immediate reconfiguration of the cramped and inadequate adult area on the first floor to create a diversity of seating arrangements and a new area for teenagers. The next four phases will build on the first-phase changes and, with public input, update, expand and upgrade the spaces for library patrons and the staff. Library service was established in the South End in 1877. The Branch was located in the Mercantile Library Association until 1879 when it was moved to the English High School. In 1904 the Branch relocated to 397 Shawmut Avenue and then again in 1923 to the John J. Williams Municipal Building at Shawmut Avenue and West Brookline Street. On June 7, 1971 the South End Branch Library moved to a new building at its present location, 685 Tremont Street between Rutland Square and West Newton Street, which previously was the site of the Mercantile Library Association.

The current building and the park were designed by the prominent architectural firm of Mitchell/Giurgola, originally from Philadelphia, but since split into two firms, one of which was established in New York City. The current library was opened in June 1971. The library was last renovated in 1996 when an elevator was installed.

In 2007, a group of residents living around the library and its park had become alarmed by the deterioration of the library site and the instances of drive-by shootings at Tremont and West Newton Street. They created a 501©3 charitable organization, the Friends of the South End Library (FOSEL), and began to lobby for a library renovation that included the visual and functional integration of the building with its adjacent Library Park. In 2008, an architect and supporter of the Friends of the South End Library drew up a partial plan that could serve as a jumping board for a proposal that would visually and functionally integrate library and park, as per below. Shortly thereafter, FOSEL was swept up by the successful citywide 2008 battle to prevent the City of Boston from closing up to a third of its branches and the renovation plans were put on hold. Since then, FOSEL has concentrated on developing programming at the library to broaden its reach into the community by, among other things, establishing the successful  authors series, The South End Writes, organizing summer jazz and blues concerts, funding children's performances and putting together the very popular annual Easter Egg Hunt.