Andy Macfie has stepped down as managing director after 14 years to become chairman.
Long-serving executives John Berthinussen and Calum Cusiter have been appointed co-managing directors.
Sir Brian said: “When Andy and I launched Souter Investments in 2006 our vision was to create a professional but entrepreneurial family investment office, building a diversified investment portfolio that would generate healthy returns over the long-term, be resilient to economic downturns and fund charitable donations. Andy has been critical to us achieving these objectives.”
Mr Macfie said: "Calum and John have worked for me at Souter Investments for the last 12 years and thoroughly deserve their promotion.