Chris Rumfitt, MD of the agency’s growing public affairs practice, is set to depart at the end of January.
It is understood that the venture – not yet publicly named – will focus on corporate comms, strategy and public affairs and involve a small number of other senior practitioners.
Rumfitt’s imminent exit follows nearly six years at the agency, where he has overseen a near doubling of staff in the public affairs practice to a team of more than 20.
During this time, he also increased its focus on property and planning, including controversial work helping obtain consent for the £8bn transformation of Earl’s Court with developer CapCo.
Rumfitt, who declined to comment, started his career as a parliamentary researcher and then Number 10 press officer and joined Edelman having headed up external comms at Network Rail.
His departure was described as a "big loss" by one agency rival, while Edelman general manager Alex Bigg said: "We’re very sad he’s going. He’s been a great servant to Edelman and we wish him all the best."
Edelman is understood to be mid-way through recruiting, with an external replacement to be announced in due course.