Diarmuid Gavin was born on 10 May 1964 in London to Irish parents Joan and Jack, and was brought up in Dublin, Ireland. His father John died in 2011. Diarmuid was the second oldest of five children — two brothers and two sisters.

Tragedy struck early in his family in 1971 when, aged just six, he witnessed his younger five-year-old brother Conor being killed by a car on the way to school. Following this, he became a shy and withdrawn child. He would build dens with his sisters and started his own garden on some waste land, shunning his parents’ conventional suburban garden style.

He received his primary education at St. Joseph’s Boys National School in Terenure, and his secondary education at Templeogue College. He then applied to the College of Amenity Horticulture at the Botanic Gardens in Glasnevin, Dublin, failing the first time but eventually securing entry. After working at a garden centre and as a florist, he established his own garden design business.

His modern vibrant city garden at the RHS Chelsea Flower Show in 1996 caused quite a stir and led to a career in television, where he developed an individual style in contemporary garden design. For eight years, his main programme Homefront was broadcast by the BBC.

In 2026, Gavin co-hosts the six-part series Greatest Gardens with Diarmuid Gavin and Carol Klein, produced by Waddell Media for BBC Northern Ireland, airing on BBC One Northern Ireland and BBC iPlayer. He lives in County Wicklow with his wife Justine Keane, whom he married in 1995, and their daughter Eppie.