The newly released visuals and details reveal Mecanoo's intentions for the Stephen A Schwarzman Building – the library's main branch at Fifth Avenue and 42nd Street – which the studio has developed with local practice Beyer Blinder Belle.
The masterplan reconfigures the historic building to increase its publicly accessible space by 20 per cent. Only a third is currently open to the public.
Underused spaces like former staff and storage areas, and some of the library's decorative rooms, will be transformed into places for research, exhibitions, and educational programmes.
"We have developed a masterplan that inherently adheres to the logic of a beaux-arts building," said Mecanoo architect Francine Houben.
"Our changes are both subtle and clever – to direct the flow for different user groups, for example, or to improve the quality and function of currently underused spaces."
The New York Public Library released visuals outlining the masterplan to garner investment for the project, which will be completed in two stages between 2018 and 2020, and is estimated to cost $317 million (£240 million).
Renderings show a new entrance and raised public plaza on 40th Street, which will lead into a new area for university and school children called the Center for Research and Learning.
Another new space – the Lenox and Astor Room – will host a display of books and artwork. Other additions include a cafe and an extended shop, and the introduction of a permanent exhibition space in the library's existing Gottesman Hall.
By teaming with Beyer Blinder Belle – a firm known for its historic preservation – Mecanoo will seek to complement historic elements of the beaux-arts building, designed by New York firm Carrère and Hastings and opened in 1911.
Landmarked spaces in the library include the ornate Rose Main Reading Room, the Maps, Periodicals, and Genealogy reading rooms, and Astor Hall.
"The masterplan builds on the framework of this historic building and icon of New York City architecture," said Beyer Blinder Belle architect Elizabeth Leber.
"We are seeking to instill clarity and ease of circulation, and to support new uses and programmes, while only enhancing its significant architectural features."
The library's leaders selected Mecanoo and Beyer Blinder Belle for the project in 2015, after they abandoned a controversial $300 million renovation plan by British firm Foster + Partners.
The contentious scheme proposed the removal of many book stacks in the Schwarzman building to create a large new reading room.
Mecanoo and Beyer Blinder Belle are yet to disclose how they will tackle this 175,000-square-foot (16,300-square-metre) space, which features seven floors of shelving, but will conduct a study to develop potential options and invite the public to offer their opinion.
The rest of the masterplan was similarly developed through discussions with stakeholders and a group of trustees, as well as staff, researchers and scholars.
The New York Public Library has a total of 92 locations across the city. The Schwarzman building, at the eastern end of Bryant Park, is commonly referred to as its main branch and houses more than 15 million items.
The two firms are also designing the renovation of the smaller Mid-Manhattan Library lending branch. Its completion is slated for 2020, when it will reopen as the Stavros Niarchos Foundation Library.