Mr Sandler will become chairman of Towry from June. He was formerly executive chairman of Northern Rock, chairman of Phoenix Group, and chairman of Paternoster. He was previously chief operating officer of NatWest Group and chief executive of Lloyd's of London.
He is, however, perhaps best known for leading the independent review of the UK Long Term Savings Industry in 2002, a review which led to calls for sweeping changes in the savings sector.
Mr Corbett said: "I have much enjoyed my time at Towry and wish the company and its management well. Stepping down now enables me to focus my energies on my new appointment at Numis and the other public companies that I chair. Ron has outstanding business experience and is an ideal choice as the next chairman."
Mr Sandler said: "On behalf of Towry I'd like to thank Gerald for his work for Towry and wish him well at Numis. Towry is a great business and I am looking forward to the challenge."
The appointments of Mr Sandler and Mr Unwin are subject to FCA approval.
Towry has also announced today that Geoff Unwin has been appointed non-executive director of Towry. He is chairman of XChanging. He was previously chairman of United Business Media plc and Halma plc and chief executive of Cap Gemini Ernst & Young where he led the acquisition of Ernst & Young's consulting activities.
Mr Unwin said: "I am delighted to join Towry as non-executive director and I look forward to supporting its continued growth and success".