Worth up to £292,000 over three years, the Colman Getty contract will see the agency leading on comms and PR at a local, regional, national and international level.
Subject to legal confirmation, the agency will work alongside the council's in-house media relations and marketing teams.
Birmingham City Council assistant director of culture Brian Gambles said: 'So far, we have developed a successful comms campaign generating a positive response and excitement at a local and national level. Now it is vital we continue to build on this success leading up to the opening of the new library in 2013 and beyond.'
Colman Getty won the contract following a competitive tender, advertised through the Official Journal of the European Union, which attracted tenders from all over the country.
PRWeek understands the appointment of London-based Colman Getty has been criticised by some Birmingham PR professionals.
As well as expanding on the success of the existing Library of Birmingham comms strategy, the agency will work with colleagues at the city council to help plan and deliver a series of activities to mark the official opening in 2013.