The library is creating a two-year roster covering everything from consumer PR to public affairs, with the line-up set to be announced in the summer.
The now-closed tender process offers work with the in-house team on a project-by-project basis.
Incumbents on the previous roster, which ended last year, included Porter Novelli, Four Communications, Regester Larkin and Proof Communications.
British Library head of press Ben Sanderson said: "The roster will be for when we need PR support in specific projects – whether that is getting additional creative thinking for launches of new services, or digitisation projects."
The tender is not related to the £24m review of media and digital agency needs involving a consortium of London’s major museums, libraries and galleries led by the British Library, reported recently by Campaign.
PRWeek revealed in 2013 that the British Library had appointed Grayling to handle comms for a £8.7m project to digitise thousands of manuscripts covering the history of Qatar.