Quinlan Private has said Brendan Mullin is to leave the company to establish an investment fund focused on public and private equity.
CEO Olan Cremin thanked Mr Mullin, who was a director at the firm, for his contribution to the property group.
In February 2004 Quinlan bought Powerscourt Capital Partners from Mr Mullin, who is a former Ireland rugby international, for a reported €5m.
Quinlan Private is headed by former Revenue inspector Derek Quinlan.