Wrest Park, one of the country's largest secret gardens, has lain overgrown and largely unknown for decades as part of an agricultural research centre.
The 18th century garden near Silsoe, Bedfordshire, saw commissions by Lancelot "Capability" Brown, William Kent and Thomas Archer in its time.
Consultants from the Landscape Agency will work with English Heritage on the first phase of a restoration, the Italian and Rose Gardens, which will be opened next year.
Managing director Patrick James said: "It is gratifying to know this outstanding landscape, which is relatively unknown, is to be rejuvenated by summer 2011."
English Heritage chief executive Simon Thurley added: "Wrest Park and its outstanding collection of historic garden buildings is one of the finest surviving 18th century landscapes in Britain. It is also one of our best kept secrets."