In 1835 Archbishop Vernon Harcourt of Nuneham House (Nuneham Courtenay) commissioned William Sawrey Gilpin to design and plant an 8 acre pinetum in the parkland associated with the estate. The estate was purchased from the Harcourt family by the University of Oxford following the second world war.
Although most of the woodlands of the estate were later sold off, 5 acres were reserved for use by the Botanic Garden. Over the following 30 years, the Arboretum was extended and totalled 55 acres by 1995, 80 acres by 2005.
Most recently in 2006 a further 50 acres of land on the southwest boundary were purchased. 20 acres of this has been planted up with 13,000 British native trees and 30 acres restored as wildflower meadows.
Many of the original plantings from the 1830s are still growing today at the Arboretum.