Source: Sharecast
Chalmers is currently co-head of the Global Financial Institutions Group of Morgan Stanley, having joined in 2000, advising financial institutions in the UK, Europe and Asia.
He is expected to join the group in June, allowing for a period of induction and smooth transition prior to joining the board and assuming the role of CFO once Culmer departs.
Chairman Lord Blackwell said Chalmers "brings a wealth of experience that will be of significant benefit to the group".
Meanwhile, chief executive Antonio Horta-Osorio said: "William has a proven track record in financial services and will be a great addition to the executive team. We will be sad to see George go, but are pleased to have had him in the team for the past seven years and to be able to have George and William working together to ensure a smooth transition."
Chalmers had a first class honours degree in economics from Edinburgh University and a Juris Doctor from Harvard Law School.
At 1015 GMT, the shares were up 1.3% to 58.17p.