Chris Ralph first joined the company in 2009 as its chief investment officer before taking up his most recent role as chief global strategist in January this year.
In a post on his LinkedIn page Mr Ralph said he would be staying on in a non-executive capacity as a member of the SJP investment committee, a role which the company has confirmed.
Mr Ralph said: "I want to take this opportunity to pay tribute to David Lamb from whom I have learnt so much over this period and who sets an extraordinary example that I and many others have tried hard to follow.
"Also I want to celebrate Tom Beal who is already a superb chief investment officer.
"What a year it has been for him in his new role but he has coped magnificently with everything that has been thrown at him with determination, thoughtfulness and intelligence."
Mr Beal stepped into the role of chief investment officer, one which selects external fund managers, in January when Mr Ralph made his move to chief global strategist.
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