Paul Myners, a former Labour Party politico, quit his chairman job at Huntsworth after a six-month tour of duty.
The company claims the exit is due to Myners' unwillingness to commit to the time required to carry out his role at Huntsworth.
CEO Peter Chadlington, 72, announced in August his plan to step down.
Myners was financial services secretary in Gordon Browns's government.
He served as CEO of investment fund manager Gartmore Group and chairman of Guardian Media Group.
Chadlington is a friend of Prime Minister David Cameron.
Huntsworth, which is parent of Grayling, says it will name a new chairman as soon as possible.
DJE Holdings, parent of Edelman and Zeno, launches RUTH as an independent shop named after Ruth Edelman, mental health advocate, wife and longtime business partner of Dan Edelman.
New York City PR firms make up the largest slice of O'Dwyer's 147 firm overall ranking with 33 of 40 in the New York/New Jersey area either calling Manhattan their home or having a presence there.
Subject Matter+Kivvit, which joined forces in May, has rebranded as Avoq, an integrated shop with more than 200 professionals in Washington, New York, Asbury Park (NJ), Miami and Chicago.
While PR pros stationed at in-house comms. teams and those working for agencies share many of the same objectives, they also have markedly different top priorities, according to a recent report.
Edelman is cutting 240 employees or about four percent of its workforce to cope with the cooling down of the PR sector, according to a memo from CEO Richard Edelman.
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