The Business branch opened in the City-County Building in June 1924 to make library service more accessible to those in the downtown Pittsburgh area. In 1930 it moved to the Union Trust Building. In 1944 the Carnegie Library added a Downtown branch for general adult lending services at this location, where "smoking and talking in an informal atmosphere" were encouraged. This branch closed in 1950, and services were moved back to the Main Library in Oakland.
In January 1952, the Downtown and Business Branches were reopened at 402 Frick Building; in May of 1957, the library was relocated to the Frick Annex adjoining Kaufmann's, until 1975, when it moved to the Frick Building Mezzanine.
The two agencies moved to One Mellon Bank Center in 1985. In December 1990, it was announced that due to budgetary difficulties, the Library would close its downtown location and move it to temporary quarters in the Allegheny Regional Branch Library on the North Side until the Bank Center renovation was completed. However, after intervention by businesses and many loyal supporters, the City of Pittsburgh and Mellon Bank, the landlord, reached a compromise that substantially reduced the library's rent, enabling the Downtown and Business Branch to remain at this location until it May of 1997 when a joint public/academic library was opened as the Library Center at 414 Wood Street.
The Library Center combined the Dowtown Branch and the Business Department with the library of Point Park College. The Foundation Center joined the Carnegie Library team at the Library Center in late 2002. In early 2004, the now Point Park University decided they would repurpose the Library Center space for other uses as the University Center, and the partnership was disolved.
While a new facility was being readied, the Business Department and the Foundation Center temporarily relocated their reference services to the third floor of Carnegie Library of Pittsburgh - Main. In January 2005 Carnegie Library of Pittsburgh opened their bright, cheerful, and high tech new facility to the public as Carnegie Library of Pittsburgh - Downtown & Business.