The group, in the process of moving all its London businesses into one building for the first time, has decided to scrap Burrell's role as chairman of Grayling Political Strategy.
The division will now be headed by Vivien Hepworth, who rejoins the group after a five year gap, taking the title of CEO.
Grayling CEO Nigel Kennedy said Burrell left by mutual agreement, denying that he had been made redundant.
Burrell declined to comment beyond the official statement released through Grayling that indicated he decided to step down.
'Grayling Group has now chosen to pursue a new strategic approach with greater integration of public affairs and PR and it seems best to leave that task to others,' he said in the statement.
But industry sources suggest Burrell was reluctant to leave the firm he had been with for the last 16 years.
Insiders added that Burrell was likely to remain within the PA consultancy field.
As CEO, Hepworth oversees work in Grayling Political Strategy's two units - Edinburgh-based Strategy in Scotland and Westminster Strategy in London - the agency Burrell set up as the PA public wing of Grayling in 1986.
She will also work closely with the firm's Brussels and Cardiff-based public affairs staff.
Aside from Burrell there are no other senior PA departures as a result of the reorganisation.
Hepworth previously worked at Grayling for ten years until 1997, as a member of the board handling both PA and PR clients. She is also a member of the Press Complaints Commission.