Ms Stent joined the board with immediate effect on Friday and will chair the group audit and risk oversight committee.
She was described as having “extensive experience as an executive and non-executive, both in the financial services sector and in other industries”.
She is currently chair of Marex Spectron Limited, a leading commodities broker, and is a non-executive director of Post Office Limited, where she also chairs the audit and risk Committee.
Her executive career has included senior roles at Virgin Group and Barclays Bank.
Andrew Sykes, chairman of Smith & Williamson, said: “We are delighted that Carla has agreed to join the board of Smith & Williamson.
“She brings a deep and varied experience of financial services and other sectors and we look forward to her contribution”.