McGlashan has been the interim head since January when the previous incumbent, Marin Heale, left the firm after five years with Kleinwort Benson.
At the time McGalshan was head of products and services and rather than reverting to this role when Rothwell joins, in February 2012, he will take on the position of head of strategy and development.
Rothwell is currently head of business development at Schroders Private Banking, before which he was responsible for UK private client business development at Merrill Lynch Investment Managers.
As well as working closely with another new recruit chief investment officer Mouhammed Choukeir, who joined from Morgan Stanley in October, Rothwell will also work with the corporate advisory team to develop the services they offer entrepreneurs.