His television shows (BBC2's Home Front and Home Front in the Garden) attract huge audiences and he has also presented BBC2's coverage of the RHS Chelsea Flower Show and Gardener's World Live - making him a popular household name in both the UK and Ireland, where he leads the way in popular contemporary garden design.

After studying for three years in Ireland during the 1980’s at the College of Amenity Horticulture in Glasnevin, Diarmuid started his own Dublin-based garden design business. His radical ideas gained him a number of renowned clients.

As well as his television work, Diarmuid writes regularly for various newspapers. He also lectures at schools of garden design and horticulture, and runs seminars internationally on garden design and the development of the modern garden. Diarmuid also runs a business in garden design and construction with Sean Cunningham, based in Dublin and London.

Well established as author, Diarmuid has written two books with DK - the first: Outer Spaces published in October 2003 and the second: Design Your Garden features his award winning 2004 Chelsea Garden as seen on Diarmuid' Big Adventure on BBC2.