Pomfret (pictured) joins the investment company, managed by Adithep Banabriksha, as a non-executive director on 1 September.
Pomfret stood down as Rathbones chief executive in February after 10 years at the helm. Under his watch assets under management at the wealth firm rose from £5 billion to £22 billion.
Prior to this he spent around 13 years with Kleinwort Benson as a corporate financier, venture capitalist and finance director of the investment management and private banking division.
Pomfret is also a director of the Wealth Management Association and non-executive director of Graphite Enterprise Trust.