Austin left Hillier just after Chelsea Flower Show after eight years at the company.
Chris Francis, Hillier wholesale and retail director said: "Since joining Hillier from Writtle College eight years ago, Steve has become a very able and talented nurseryman. He now joins the ranks of Hillier alumni who form the backbone of UK horticulture, and we wish him well in the next stage of his career."
Plant Marketing International owner Ed Marley said: "I am delighted that Steve is joining Plant Marketing International (PMI) in a newly created role.
"He has over nine years’ experience within the horticultural industry and prides himself on his plant knowledge and product development skills.
"His main experience comes from being a Product Manager for Hillier Nurseries, where he worked for 6 years. His main role there was building relationships with growers and breeders from around the world to gain access to new and unique products to give a competitive edge for the nursery.
"Steve is joining us in a similar Product Development role with a global remit to bring new and exciting genetics to the market. Steve will be based in the UK."