Michael Alen-Buckley, executive chairman of RAB Capital, said Mr Couttie had made a "number of significant contributions" to the business, adding that he would continue to work for the firm as an adviser "for some time".
RAB Capital was hard hit by the financial crisis and from assets of $7.2bn at the end of 2007, the firm was hit by massive outflows during 2008 that saw its total funds fall to less than $2bn 12 months later.
Mr Kirwan-Taylor joined RAB as an executive director at the same time as Mr Couttie replaced Philip Richards as chief executive and is an experienced financier having held senior jobs at Credit Suisse.