Landscape architect J&L Gibbons and contractor Gavin Jones worked on the project to restore the west London park to the look it had in its heyday in the 1800s, when it was the setting for Sir John Soane’s designs for Pitzhanger Manor and Gallery.
An opening ceremony took place on Friday when council leader Julian Bell and Mayor councillor Tej Ram Bagha joined local schoolchildren for a community kitchen garden workshop.
Committee member for the Heritage Lottery Fund, which contributed £2.4million to the project, Jon Sheaff, also attended to witness the unveiling of a bronze plaque which acknowledged the donation.
Ealing Council contributed £2.7m. A further £100,000 came from The Veolia Environmental Trust.
Gavin Jones staff restored the park’s walled garden, widened paths and resurfaced throughout.
Councillor Julian Bell said: "This project has been a labour of love for all involved, because Walpole Park is such a special place with huge historical significance, not just in Ealing, or London but nationally.
"It perfectly represents Soane’s architectural and horticultural vision and I am so grateful to the HLF for awarding us with the funding to restore his vision and make Walpole Park an essential destination for a whole new generation of park lovers."