He will address gardeners' concerns about the threat posed by pests and diseases and co-ordinate RHS activity to identify and control new pests and diseases with that of other organisations undertaking similar work.
Clover formerly managed the Plant Health & Environmental Laboratory in New Zealand's Ministry for Primary Industries and has 20 years of experience in scientific research in New Zealand and the UK, including heading a team of 45 people identifying and managing plant pests and diseases, and providing scientific services to the New Zealand and UK governments.
He said: "I'm tremendously excited about the challenge of working for the world's foremost gardening charity. I believe my experience, coupled with the skills of the hugely talented team at the RHS, will mean that we will be able to help even more gardeners identify and control garden pests."
RHS head of science Alistair Griffiths said: "Recent threats such as Ash dieback and the findings of the government's Tree Health and Plant Biodiversity Expert Task Force report graphically highlight the threat posed to UK horticulture, gardens and the wider environment by pests and diseases.
"This new role highlights the RHS's commitment to harnessing world-leading knowledge to provide authoritative and up-to-date scientific advice to advance plant health management in our gardens."