Fold7 beat off competition from BMB and The Red Brick Road. 18 Feet & Rising was also involved earlier in the pitching process, which was handled by the AAR.
Audible previously worked with a number of agencies.
Marc Nohr, the chief executive of Fold7, said: "Our brief is to raise the profile and get people to understand the role this product can play in their lives."
Amazon picked Deep Focus London to handle social content for its European fashion business following a competitive pitch last month.
The online retailer, whose website Amazon.com started 20 years ago yesterday, confirmed the appointment of Fold7 but did not comment further.