The gardens were originally designed by Thomas Mawson and were further developed by Reginald Cory when  Dyffryn House and Estate fell into his hands in 1910. A leading figure in the R.H.S. Reginald was a keen horticulturalist and plant collector.

The grade 1 listed gardens have been restored in recent years with support from the Heritage Lottery Fund.

Features of the gardens include: Great lawns, Arboretum, Champion Trees, Pompeian Garden, Herbaceous Borders, Theatre Garden, Fernery, Heather Garden, Panel Garden, Statury, Water Features.

The garden has been voted the 2nd best Garden in Wales.