The TV and phone provider had been with former incumbent Citigate for more than a decade, but has switched to the Chime Communications-owned agencies after a competitive pitch process in July.
The brief is believed to be worth about £500,000 a year and will cover public affairs, financial PR and corporate comms.
The move follows TalkTalk's split from The Carphone Warehouse last year to become a standalone company.
One source said TalkTalk was now keen to amplify its corporate voice and build a stronger corporate brand, after establishing its consumer presence with its sponsorship of The X Factor. TalkTalk uses Bell Pottinger agency Resonate to support its X Factor sponsorship.
TalkTalk's comms director Mark Schmid confirmed the appointment and said: 'We've had an excellent partnership with Citigate Dewe Rogerson for many years. It has played a big part in the TalkTalk story, from the launch in 2003 to our position today as a leading provider of phone, broadband and mobile to five million customers.'
TalkTalk was identified by Ofcom earlier this year as the most complained-about TV and broadband provider. It was hit by a record £3m fine in August for mistakenly billing thousands of customers.
The brand took control of Tiscali UK in 2009, and encountered problems switching the company's customers to the TalkTalk billing system.
The company has a new CEO, Dido Harding, and appointing different agencies could be viewed as a bid to move the brand on from issues that predate its independence.
Schmid said the firm wanted to consolidate its agency relationships under one roof, but added that Citigate would continue to work on several projects, including its Digital Heroes Awards.
Pelham Bell Pottinger MD James Henderson will work on the brand's financial comms, Bell Pottinger Public Affairs MD Tim Collins will handle public affairs, and Good Relations' Steve Marinker will look after corporate PR.