She will do so at the end of the year after helping re-shape the future of the charity.
Ms Grimsey helped the body in its decision to create a new role of deputy director-general – which will be filled by Gordon Seabright.
“Gordon is a valued colleague whom I have worked with since I joined the RHS,” she explained. “I look forward to working more closely with him in implementing the RHS change programme.”
Mr Seabright is currently employed as commercial director at the society and is also group managing director of RHS Enterprises – the charitys trading arm.
He explained he is looking forward to working in the new role, adding it shows the societys ambition.
The RHS hosts numerous events throughout the year, including the Chelsea Flower Show in Lond