Proctor is likely to leave in the first quarter of 2012 to take up a position of executive general manager at Commercialbank of Qatar.
He has given notice and the board of Arbuthnot has already agreed terms with his successor, who will be appointed once regulatory approval has been obtained.
Proctor has been with the group for three years and has worked mainly on accelerating the development of Arbuthnot Latham & Co, the private banking arm.
The group said Arbuthnot Latham had grown significantly in both volume and profitability since he had been CEO.
Henry Angest, chairman and CEO of the whole group, said: "Dean Proctor made an outstanding contribution to the group throughout his time at Arbuthnot Latham. His management skills are exceptional and I am sorry to see him leave.
"In the last few years I have commented on my concern that the pre-eminence of the City of London and the UK’s financial services business will be damaged unless steps are taken to ensure that the business environment in which it operates remains competitive.
"Dean Proctor leaving to pursue his career elsewhere in the world is to me a further example of the danger of not maintaining a strong enterprise culture in the UK."
