The three-year account is believed to be worth up to £300,000 and could be extended up to five years.
A campaign will aim to increase FETA's interaction with the media, develop stakeholder understanding and improve communications with the public.
FETA, whose main function is to operate and maintain the Forth Road Bridge, appointed Chris Waite as its first comms manager at the end of January.
From a shortlist of six, CM Porter Novelli beat Weber Shandwick, Media House, the Big Partnership, Consolidated Communications and Pagoda PR.
The company used Weber Shandwick for interim support during the pitch process. Waite said he felt Porter Novelli could provide ‘more streamlined and integrated support'.
FETA wants to educate the public on how the toll charge is spent, and emphasise that the maintenance that causes traffic disruption is essential, said Waite.
The body is currently considering how to slash congestion in the long term, either with a second crossing or by replacing the bridge - the main road link across the Firth of Forth between Edinburgh and northern Scotland.
Director Ann McMunn, who will manage the account, said CM Porter Novelli will also be involved in increasing public awareness of the new electronic toll systems.