FitzPatrick has led the change and internal comms division since helping establish it three years ago.
PRWeek understands that he will launch his new agency later this year, though a name for the company is yet to be confirmed.
Current senior consultant Cami Joerin will replace FitzPatrick to head up the practice, which offers clients internal comms specific services.
FitzPatrick rejoined Bell Pottinger to lead the team in 2009, having run his own specialist consultancy Working Communications.
He had been with Bell Pottinger several years earlier but left to become global head of internal comms for Marconi.
He is also well known for running the Black Belt boot camp comms training programme.
FitzPatrick, who reports to Bell Pottinger chairman David Wilson, said: ‘It’s been a great three years working with David Wilson and David Beck – I am massively in their debt for their support and their guidance. However, I have come to the conclusion that I want to operate in a more focused way on change communications and feel that returning to my independent practice will enable me to concentrate more fully on the work I love.’
Wilson added: ‘Liam’s done a great job establishing the change and internal communications practice, and we’re delighted that Cami’s agreed to take over. Cami’s excited about continuing to develop the practice as a centre of expertise to support our Bell Pottinger Private clients.’