Talk PR won the account following a competitive pitch process, overseen at the start of the year by Kate Saxton, PR director at FCA.
Saxton said: "We were impressed by Talk PR's creative ideas and can-do attitude. But most of all we loved the fact that they really got under the skin to discover what the Fiat brand is all about and presented ideas on how to make those Fiat truths resonate with key target audiences."
London-based Talk PR was 53rd in PRWeek's Top 150 UK agencies for 2015, and had a 2014 fee income of £4.2m. The lifestyle agency works for clients including American Express and The British Fashion Council.
FCA also owns car brands Alfa Romeo and Jeep, and last year decided to combine the UK comms briefs for these two brands within a single PR agency. It appointed Performance Communications, which previously managed PR for Alfa Romeo. McCann had held the Jeep account prior to the reorganisation.