Grade II-registered Caversham Court Gardens became neglected during compulsory competitive tendering, a report from Reading Borough Council said. A lack of capital funding and cash for maintenance led to deterioration of the site, according to the council's management and maintenance plan.
But via the restoration project, a full-time gardener was employed to look after the gardens and plan a horticultural training programme for staff and volunteers.
The scheme was designed by landscape architects from Hampshire County Council and carried out by contractors from English Landscapes. More than 3,000 people attended the opening celebration on 7 August, including head of the HLF South East region Stuart McLeod and representatives from the Friends of Caversham Court.
McLeod said: "We are delighted to see Reading's most historically significant gardens open again after the major restoration works. Now they can be enjoyed to the full by the local community, who have been so involved in the fruition of this project, and visitors alike."
Work included the restoration of 17th- and 19th-century features, the gazebo and its causeway, a serpentine retaining wall and the ancient yew family.